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Old 04-01-2021, 11:56 AM   #1
hbr509
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Bottom Material

I have a 2021 3931fb The material under the chassis sags about 8-10 inches in the center ,its only attached on the sides of frame is this normal? Thanks
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Old 04-01-2021, 06:15 PM   #2
Cbrez
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Some sagging is normal. Water lines and some electrical cables are unsupported and just laying on top of the coroplast, causing it to sag. 8-10” is a bit much though. I’d take a corner down and push up on the low point of the sagging area to see if anything comes out. Could be a water leak causing the sagging. I found a gray water leak from our shower this way.
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Old 04-01-2021, 06:49 PM   #3
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Do a search for removing underbelly material for various ideas for how to remove the power driven pins/nails and replace with self tapping screws.
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Old 04-01-2021, 06:53 PM   #4
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That's a bit much. Poke a small hole through the lowest point and see if fluid comes out.
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Old 04-01-2021, 08:59 PM   #5
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That's a bit much. Poke a small hole through the lowest point and see if fluid comes out.
I would not drill into the Coroplast.or at least I’d be very careful about doing it. I’d worry about hitting a water line or waste water tank sitting above the covering . Removing a few screws to drop a corner of the coroplast is really an easy and safe thing to do.
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Old 04-02-2021, 04:08 AM   #6
hbr509
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Thanks for the replies ,I will take a peak and see what the deal is . I would have thought there should be some cross supports . I'm probably over thinking this . OCD again
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Old 04-02-2021, 06:58 AM   #7
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You can also hit the low point with your hand. If it feels fairly solid and not flexing, it could be holding water. If so it would be good to drain it out soon. Pushing a thin phillips screwdriver of similar object through it less than half an inch will cause no harm. Let us know what you find.
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Old 04-02-2021, 07:09 AM   #8
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All four of our montana units have had cross support beams for the underbelly.
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Old 04-02-2021, 11:49 AM   #9
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All four of our montana units have had cross support beams for the underbelly.
Ours has none and hangs down pretty far as well. Adding them is on my "to do" list.

I don't see them here either 3:04 :

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Old 04-02-2021, 07:01 PM   #10
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All four of our montana units have had cross support beams for the underbelly.

Our RVs with coroplast have had cross beam supports. Trying to support 8' of coroplast with stuff laying on top from the edges is not good. OP needs to drop a spot and see what's what; just sagging or something laying on it - stuff or liquid or....
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Old 04-07-2021, 01:04 PM   #11
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Two inches of sag, okay. What you're describing is a lot and I would suspect water from a leak.
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Old 04-07-2021, 05:35 PM   #12
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i just replaced all of the insulation and the coroplast on the front of my 3455SA and it was very easy to do by myself with the help of a couple of jack stands laid on there side to push up the channels that hold up the coroplast . still sags a ;little in the front and rear where there is no channel. looks like new. I could only find white coroplast but it is on the bottom so no problem. got all material at home depot
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Old 04-07-2021, 05:39 PM   #13
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there is a hugh hole in the front compartment that all of the hydraulic line and electric lines run through and needs to be plugged to keep rodents out of the insulation and coroplast, there was a lot of critter crumbs on top of mine.
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Old 04-08-2021, 06:27 AM   #14
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When I pulled down the corner of my underbelly, water actually dripped out of the coroplast from the sides...rain water must have made its way into the plastic through the exposed holes at the edges. That added to the sagging. I ended up adding two 6-foot cross members to hold up the belly and move the low spot.

You should be able to see what is in your underbelly by going through the basement storage compartment and taking down the walls that separate the basement from the furnace area. What I found when I did that was a lot of junk left behind by the manufacturing process, including wiring pieces, screws, water and hydraulic fluid pooled at the low spot. Yes, there are some wires and hoses running through the belly, but not at the low point, so I drilled a small hole and let the liquids drain out.

The water was from a leak in our shower drain that I patched with additional caulking.

I have a large suspicion that the hydraulic fluid was also a mistake from the manufacturing process. As a full-timer I move almost every week and have never had to add fluid to our reservoir. If it were a leak at the slides or jacks, I would have seen the fluid level drop, which is not the case. My suspicion was also mostly confirmed by visual inspection when my partner closed and opened the slides several times while I watched...no new fluid was found.
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Old 04-08-2021, 06:30 AM   #15
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I have two cross braces under mine. They are under the two holding tanks ( black and shower). I've always thought the braces are not to hold the coroplast up but to catch the tanks if they drop too much.
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Old 04-08-2021, 08:26 AM   #16
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After getting IS - it will be tough to change coroplast as the two cross members sit up very high.
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