Well, here's my thoughts, which are many, and this post will probably be long.
Let's compare the two campers under question:
373RD (High Country) click here
Shipping Weight 12848 lbs
Carrying Capacity 3152 lbs
Hitch 2530 lbs
3791RD click here
Shipping Weight 14119 lbs
Carrying Capacity 2481 lbs
Hitch 2620 lbs
Camper 373RD total weight capacity is 16,000 lbs
Camper 3791RD total weight capacity is 16,600 lbs
If loaded to max capacity (weight), both of these are going to be over any "comfortable" towing experience with a 250 gasser. If you are truly serious about either one of these, you are in 1 ton truck territory. The gasser 250 may pull it, but it will be one very disappointing experience.
About the models themselves. A lot of folks love the center island, but seriously look at both floor plans and ask yourself, which one has the most counter space. You will see the one without the island has more space. Plus, the stove top will have a cover which extends the space even more.
We have a 375FL and the kitchen sink, stove, and counter is set up like the High Country (no island) and the kitchen is great! Lots of space, lots of counter space, and everything ... everything ... in the kitchen is accessible with the slide in. The island chops up your space, and for us, it made us feel claustrophobic. It's something to think about.
With slides "in" neither camper will allow access to the rear living room without climbing over something. With slides "in" neither camper will allow access to the pantry cabinet.
The 3791RD has only 1 sink in the bathroom, but the toilet is turned, giving better room for men, when they sit down and spread the knees. (a gentleman's bathroom)
The 373RD has 2 sinks in the bathroom, but more limited space on the "thrown". (a lady's bathroom.)
Both showers are the same identical size.
The Montana has a higher MSRP price than the High Country.
The High Country is one foot longer than the Montana.
Both campers have 2 raised ends with the kitchen in the middle at the lowest level. It doesn't matter if you have the heat or the air conditioners on, you will never get all 3 floors the same temperature. Even in ours, that has a front living room and is open from the front to the kitchen, the difference in temperature is always different and noticeable, and we have no wall between the two rooms.
Our floor plan, click here - 375FL
However, I do envy all the outside storage space in both of your models that we don't have on ours. Just beware, your campers are probably advertised 4 season up to zero degree weather .... and they are. But, about half the heat generated from the furnace goes into the outside storage areas and under belly to keep water lines and holding tanks from freezing. They use an incredible amount of propane to heat once the temperatures drop to around freezing, because electric heat from the heat pump or the electric fire place does not get pumped into the cargo bays or the underbelly. Only the furnace blows heat into them. And these Montanas use a LOT of propane to keep heated comfortably and to keep stuff from freezing up.
Well, enough of that.
About your tow vehicle? I pull mine with a 1 ton diesel dually crew cab. Suffice it to say, mountains, flats, ocean side, or desert, towing is sweet! And I'm on my 3 rd 3500 dually. The first was a gasser towing a much smaller travel trailer and I found myself having some hair raising disappointments with it. The next was a diesel dually, long bed crew too, and I never looked back.
First diesel, frame and doors rusted out.
Second diesel, the fiberglass fat fenders spider cracked and I was concerned one day they would just simply fall apart.
Third diesel (my current one), purchased brand new, all metal body, has the integrated brake controller, nice bells and whistles and tows like a beast!
You really need to rethink your tow vehicle if you really want to tow comfortable. You will be pulling a massive monster behind you! You truck needs not only the towing abilitty, but the ability to carry the load in the bed of the truck without squatting horrible, and also needs to be able to have enough braking power to stop both the truck and trailer (if and when) you have trailer brake failure. It takes only 1 time for the trailer 7 pin plug to unplug and then you have no brakes. What happens when that idiot moron pulls out right in front of you and you slam on the brakes? Can your truck alone stop the entire rig? You have only 1 try and maybe never again if the truck, by itself, can't stop you! Think about that. $150,000 to $175,000 dollars just slammed into another vehicle, and your fifth wheel is now in your back seat.