We have camped in 100+ degree weather and were able to stay pretty comfortable, but it was very dry heat in Colorado. When we took the camper to Corpus Christi this summer, it was extremely hot and extremely humid, and the A/C was only able to keep us in the low 80's inside the coach. The front room was pretty warm, the kitchen/dining room was around 80-83 or so, and the loft was cold. As soon as the sun went down, it really wasn't hard to stay cool indoors.
I think this floorplan might be a perfect candidate for the RV Airflow Systems solution. It's a device you install inside the A/C cover and it forces more air into the duct work in the camper. It disables the air dumps on the A/C cover, and improves the efficiency of the air being pushed into the rest of the coach. I haven't tried it yet, but from my experience with this unit, I think it probably makes good sense. I would encourage you to research this solution.
I also can agree with an earlier comment about the fridge in the extreme Texas heat not keeping up very well. I have the 376FL, so I have the RV fridge, not a residential-style fridge. The fans seem to be insuffencient on the rear of the fridge, and while the freezer did reasonably well, the fridge could only maintain upper 40's and lower 50's. We put a small fan inside the fridge, which helped a little. But a future project will be to improve the air circulation on the back of the fridge.
Back to the interior cooling issue, I found that fans make a big difference in keeping comfortable. RVs, in general, just don't circulate air all that well without a little help. I keep the air dumps open in the loft and put a powerful fan right at the top of the rail to blow it down into the hallway area, and that makes a huge difference for us. We also put fans up front on the half-wall to blow air up into the front room.
For me, camping in dry heat isn't a problem. Extra circulation with fans is really all that was needed to keep us in the 70's inside. But in humid heat, it was tough to keep comfortable, especially in the front room. I think the RV Airflow device will help a bit in the future. I plan to order one soon.
As for the tail dragging issue, yes unfortunately I am towing with a 4x4 short bed (Ram Mega Cab) and the truck is a little too tall. I have everything adjusted as low as it can go, and I still can't quite get it level. After lifting the trailer a couple of inches, it's a lot closer to level than it was before. When the unit was delivered, the driver was in a 1-ton Chevy dually, and it was very level with his setup. If you have a long bed and don't need an auto-sliding hitch, that will help level it out too. My hitch is a little high because of all the moving parts in the auto slider.
I am now chasing a small leak in the rear driver-side corner of the unit. When we were in Texas, the condensation from the A/C started to come into the loft through a ceiling outlet. After some investigation, it looks like it might be coming in behind the gutter. Sometimes I really wish we didn't love this floorplan so much because it has been a pretty huge pain in many ways. I blame the fact that I ordered it just as COVID hit the factories, and I'm sure it caused a lot of disruptions. Our unit was due in May that year, but we didn't get it until September due to supply chain disruptions. That's forgivable, but the abundance of problems we've had with ours sure doesn't make me eager to buy another Montana. My wife says I'm not being fair about it, and while it's true that it's not unusual to be in a somewhat pursuit of projects and repairs on these things, I've never had to go to the lengths I've gone on this one.
I think my next fifth wheel is going to have 3 A/C units so we're not hot, and it won't have the drop frame at the rear so I'm not afraid to take it anywhere. Even after the 2" lift, I've whacked the tail on the ground a couple of times. It's WAY better than it was at the stock height, but still a little tricky when you come across that steep dip at an intersection. To me, it's just not practical for a coach this long to be that low at the rear.
After saying all this, it is still one heck of a cool floorplan.