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Old 07-28-2022, 01:26 PM   #1
QuincyAt4M
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Insulating the Underbelly and Tops of the Storage Compartments

I bought a 2021 Montana 3761 FL a few months ago. It has two 15,000 btu Coleman Mach 15s in it with the prep for an additional unit in the kitchen ceiling. During the heatwave we have been having, the temperature outside has been 100-104 F during the day. The temperature in the RV would get up to 84-86 F.
I noticed that when I went into the storage compartments underneath it was very cool in there. I was about to make arrangements to install the third A/C when I had this thought:
The way the 2" aluminum framework is in the top of the storage compartments is perfect to have it shot with 2" closed cell foam insulation. This insulation seals all cracks and is extremely waterproof. Also the never-ending battle of the under-pinning made me think also about having it shot under the RV also. We have it off right now repairing some tank level sensors. I would consider shooting the water-proof foam on the underside, tanks etc. but installing block-outs around the tank heads where the sensors are, installing some 2 inch wiring chases by splitting PVC pipe and bundling wires (without taping together so they can be fished out and in later if need be) and doing the same with any small hoses like tank flushes. Where these block-outs are I would re-install the under-pinning with 2" of the spray foam shot to the back (inside of it).

Now the 64 dollar question.... does anyone know of a reason not to do this? I believe I would not need to install the 3rd AC unit if it was sealed and insulated as described. If it came to it one day to have to dig out a tank to be changed, I'm not opposed to that.

Your technical thoughts are appreciated.

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Old 07-28-2022, 01:41 PM   #2
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Quincy, I wouldn't spray the underside. Too much stuff under there that may require access later. As far as on top of the storage compartment many have just bought two-inch insulation and cut it to fit tightly between the framing. Think that would be cheaper than the spray foam though not as airtight. Search the form. There are many threads on what people have done to stop air leaks on their rigs. If you have the return air vent under your steps, sealing that during the summer will stop a huge loss of cold air to the underbelly.
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Old 07-28-2022, 01:54 PM   #3
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After our second year with our Montana High Country, I realized how many gaps there were between the Chloroplast and the frame, J-panel, and connecting places under the trailer. I realized this when I opened up the front pass through, removed the back wall, and in the dark under there, I could see all the light coming through from outside. I used a combination of Liquid Nails and Foamy "Stuff" and sealed up every inch under the trailer.

Result? first, the furnace doesn't run as much. Second, in the winter we don't have that cold draft blowing across the bottom floor, especially near the steps were the furnace return is located at those grates on the steps. Third, the AC seems to be working much better. After 4 years, I am still finding gaps inside the camper that is exposed to the underbelly. As I find them, I'm sealing them up too. Little by little, the AC seems to be doing better.

Now, about the cool under the floor? A couple weeks ago I realized I had a drip on my grey water (shower) drain pipe plumbing under the trailer. I was able to remove all the foamy Stuff around that pipe where it came out from under the trailer and there was a hole big enough I could stick my hand in and re-putty the pipe (which did seal it, so all is well).

But, I also noticed, as soon as I got that foam removed from the hole, there was a steady breeze of cool air coming through that hole. So, somewhere in the camper, the air is still being pushed from the AC's on the roof, through holes in the floor and under the floor. Maybe it felt cooler under there because the space is smaller, and under the floor in the shade of the trailer where the sun never beats down on.

To answer your question? Well, I really cannot. I've never tried what you are asking about. I do not see any reason why you could not do it. But, I really do not know how much it will help cool the inside of the coach, or how much difference it will make.

On the other hand, I do see how your idea would really affect heating the underbelly in the winter months, since all the pipes and tanks depend upon the air from the furnace blowing under there?

If you are not a cold weather camping person, then your idea is plausible.

if you want to add more insulation, the best way, (in my opinion) would be to remove the underbelly Chloroplast, lay some foam board insulation in there between the frames, and then put the Chloroplast back up. This would help insulate more and would still allow the furnace to blow under there. But, is the time and cost to do so really worth it? it all depends upon how much you use your camper and under what conditions.
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Old 07-28-2022, 02:44 PM   #4
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What has worked the best for us is shading any window that gets sun on it. We use the awnings on those we can and snap-on sun shades on the rest.

Sun shades must be on the outside as Reflectix on the inside is all but useless as the glass and frames get too hot to touch unless covered entirely on the outside. There is a company around Quartzite that will come to you, measure, make and install them.
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Old 07-28-2022, 03:13 PM   #5
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Thanks to each of you for your input, all are valid points and suggestions. I just crawled from under the RV after my guys got all of the chloroplast off and what little batt insulation out that there was. Only about 50% of the under floor batt insulation was installed. What was there was pushed around and wadded up like someone had a wrestling match under there. The other upper insulation with the black covering between the flooring and the frame has been slashed in multiple places where pipes or wiring penetrated the floor. Where a 2" slit would have done there is a 12"-16" cross slashes exposing significant portions of the flooring. I would use the terms cable and hose management but that would not apply here. It is the most horrific mess I have ever seen. With a 45 year history in plant maintenance, electrical and mechanical design I could not have done a worse job if I was blind, deaf and dumb.

Question: The vents that are in the underbelly, is that for heating or is it for humidity/moisture removal? How do they work?
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Old 07-28-2022, 05:53 PM   #6
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Those are heat ducts.
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Old 07-28-2022, 06:46 PM   #7
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When you take down the basement walls you will find one duct laying on the floor. Take that one and put down at the back of the tanks pointing towards the valves to help prevent freezing.
As far as keeping cold air in, we put Magnetic register covers over the floor registers.
I have also made covers for the stair vents.
We remove these in the winter for the furnace to work.
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Old 07-28-2022, 07:07 PM   #8
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Ok, I'm against insulating the cabin from the basement as the furnace air return goes through the stairs, the basement and back to the furnace.
It helps keep the pipes from freezing.

By all means insulate the walls and floor (add more reflectex ABOVE the coroplast).
I added two 1" layers of styrofoam board to the floor and walls of the battery compartment (lithium batteries don't like being freezing cold when charging).


Air gaps:
The real problem with heating AND cooling

Look under your frame. There are lots of holes and gaps. This allows cold (or hot, summer time) air into your underbelly and can freeze your pipes.
Use gorilla tape to close off any small openings (hydraulic lines, slide cylinder).
Use aluminum sheeting and cut to fit around the hydraulic jacks. Leave the opening around the propane tanks. They must have ventilation (safety code).
Take down your basement walls, crawl in and close the doors. You will see daylight coming in through all the gaps along the frame.
Look behind the convenience center towards your middle jack. Very large opening where the jack comes through. To close this you will need sheet aluminum cut to fit.
Some have sprayed styrofoam on the inside of the J channel skirt to insulate the frame.
There is a panel under the bottom shelf in the pantry. Behind the panel is the water heater. Again you can see daylight coming in around the edges. This requires fire retardant insulation around the water heater to block out the air gaps.
Under your kitchen island there is a panel covering your plumbing. Take it out and there is a big Triangle gap in the corner. Cut and fit styrofoam to fill the gap tight. Use gorilla tape to seal it in place
Just remember, if your pipes ever freeze, you can put a hair dryer down this hole to put heat into your underbelly to thaw the pipes.
Under the bathroom sink you will also find air gaps where the plumbing goes through the floor.
Remove the drawers closest to the fridge. At the back where the propane and electric wiring come through to the oven, there is a gap in the wall by the fridge. Remember the back of the fridge is vented to the outside. Cold air comes in through this gap. Mine is an RV fridge so I have to be careful because on the other side of that wall is the chimney for the fridge heater. I have to use flame retardant insulation here.
Look up in your hitch pin box, you will see your bedroom closet floor and a hole where your 7 way cable goes through the frame. I taped up the hole and wedged 2" styrofoam board up against the floor.
Look at the inside door frame of the pantry. You will see a gap. This leads to the basement.
Make sure your inside and outside slide seals are good.
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Old 07-28-2022, 08:09 PM   #9
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cold basement

If you cover the vents built into the living room stairs, I found that to be the case in our 3761FL. I removed the pass thru cover and installed bubble wrap on the backside of them. it will work wonders. the basement doesn't get so cold anymore. and it was an easy fix. JUST DONT FORGET TO REMOVE BEFORE YOU TRY TO USE THE FURNACE! That is the cold air return for it.
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Old 07-28-2022, 09:02 PM   #10
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Going to workÖ.

Thanks for the helpful advice. I will be implementing many of your suggestions and then evaluate the results. Although not new to RVs, this one is very different from my 2008 RP299. Your replies will definitely save me a lot of time and trouble.

Thanks again.
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Old 07-30-2022, 11:03 AM   #11
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Hello, check out ez snap. We use to live in Fla and this really helped. When we go back in the winter it goes on. Ours is 10 years old now and the mesh is in like new condition
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Old 07-31-2022, 01:27 PM   #12
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Quote:
Originally Posted by R.S.O'Donnell View Post
What has worked the best for us is shading any window that gets sun on it. We use the awnings on those we can and snap-on sun shades on the rest.

Sun shades must be on the outside as Reflectix on the inside is all but useless as the glass and frames get too hot to touch unless covered entirely on the outside. There is a company around Quartzite that will come to you, measure, make and install them.
I made my own using solar screen and the aluminum framing. They are attached using industrial velcro type self adhesive squares on the window glass.. Blocks 90% of the light and radiant head and uv rays. Was an easy project, just a bit time consuming. Have been in Galveston with a strong on shore breeze and they have been holding strong. You can still see out so itís not like living in a cave. REALLY cuts down on heat coming through the glass. Big difference in cooling. Only takes a few minutes to put up. Cost me under $200 for materials. I have a lot of windows in this 5er.
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Old 07-31-2022, 02:17 PM   #13
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As mentioned above, keeping the sun off the dark window glass is important.
Here's a test I did using reflective window film

https://www.montanaowners.com/forums...57#post1224357
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Old 07-31-2022, 03:26 PM   #14
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Mike,

Could you send some pictures when it’s convenient? Very interested in doing that. Front and back of a screen and the Velcro on the RV please.
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Old 07-31-2022, 05:59 PM   #15
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X2 Mike - please post pics!
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Old 07-31-2022, 07:27 PM   #16
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Wow way to much work. We were in the the stifling heat on the East coast all last week in the Boston area. I just went to Walmart and bought 2 5000 btu window units and put one in the bed room and one in the living room and it was enough to cool the unit down all day with the 2 big A/C`s running. I know it looks a little Sandford and Son having window units hanging out the side of the camper but looks better than covering all the windows with a material of some kind. I cant deal with the heat trying to sleep. Some on want to remind me why we should have to do this kind of stuff on a 100,000 dollar camper.
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Old 08-02-2022, 01:27 AM   #17
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Can I copy your design?

Quote:
Originally Posted by Mikelff View Post
I made my own using solar screen and the aluminum framing. They are attached using industrial velcro type self adhesive squares on the window glass.. Blocks 90% of the light and radiant head and uv rays. Was an easy project, just a bit time consuming. Have been in Galveston with a strong on shore breeze and they have been holding strong. You can still see out so itís not like living in a cave. REALLY cuts down on heat coming through the glass. Big difference in cooling. Only takes a few minutes to put up. Cost me under $200 for materials. I have a lot of windows in this 5er.
Mike, if your still out there and have the details on your design, I would appreciate diagrams and details so Ok can make these for my unit.
Remember....KISS... Keep it simple so I can understand. I read pictures much better than text. :-)

Thanks for anything you have.
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Old 08-02-2022, 09:25 AM   #18
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Originally Posted by RBul31 View Post
Mike, if your still out there and have the details on your design, I would appreciate diagrams and details so Ok can make these for my unit.
Remember....KISS... Keep it simple so I can understand. I read pictures much better than text. :-)

Thanks for anything you have.
Ok, Iím back. So you need to go to HD, or Lowes, go to where they have the screen supplies and purchase some 7í screen frame in either white or brown. I think those are the only colors. My guess is you will need a minimum of 4. Any unused you can take back.. Your solar screen is there in rolls as well. First, measure each window accurately, the glass only. Triple check your measurements! Figure out how much length you will need and buy the appropriate length roll. You might need a second smaller length roll but wait and see. My slide out windows have frames so thats why I measure only the glass where you will cover with the screen. Measure each window and write them down. The longest part of the window is where the frame will go so some windows might have frames vertical, some horizontal . This is to give the screen the most support. You are only using frame on two opposite ends. When taking them down you can roll them up. You will need a spline tool to insert the spline and they are cheap. You will need a large table to roll out and work on your screen. You will also need something to cut the frame to size. I used my jig saw with a metal cutting blade. Remember the outside edge of your frame should measure the dimension of your window measurement. Find something to hold your frame in place while you fit your screen and insert the spline. You should have an inch or more to trim. Your accurate measurements are key. Insert the spline and trim excess. I leave any excess on the UNFRAMED sides to overlap the windows. The velcro type heavy duty self stick come in 1 inch squares. The large windows will need 2 of the 1 inch squares on each end and one on the middle on the top end, with 2, 1 inch squares on each end at the bottom. Small windows can get by with 1, 1 inch squares. Only problem so far Is the windows with frames still heat up and still get quite hot. I didnít want to put that velcro on the frames as they could be problematic getting them off. Glass is easier using some adhesive remover like goof off. I am going to test using some Reflex it on the tops of the windows and solar screen on bottom half. The reflex tix can cover the entire frame while attached to the windows. Iíll post pics later.
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Old 08-05-2022, 08:52 AM   #19
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Has anyone used a window film? https://www.amazon.com/HIDBEA-Privac...315327763&th=1
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