I've read many posts on "what length RV should I buy", and they always include all kinds of arguments for a small/short RV and all kinds of arguments for large/long RV.
Folks who prefer a small/short RV list several advantages - but this one is rarely talked about: A small/short RV is easier to keep cool (...and warm) using common RV appliances.
We have a 24 foot Class C motorhome with a 13.5K rooftop A/C unit and a full ducting system running the length of the RV (even including one ceiling duct in the bathroom and one ceiling duct above the cabover bed). Each duct can be rotated 360 degrees to aim it, and opened any amount to control it's air flow.
For extreme daytime heat we have a curtain to block off the cab area, a curtain to block off the cabover bed area, and a curtain to block off the rear bed area ... such that the 13.5K A/C only has to cool an area a little larger than a truck camper. With a 13.5K A/C and that kind of interior volume control, the resulting downsized living area can indeed be kept cool.
We have made an extensive RV trip in the Southern U.S. in July/August and had no problems at all keeping cool - including looking for rocks in remote areas of the scorching Texas Panhandle. Throughout the Southern U.S. at that time of the year in those temperatures and humidities we of course had most campgrounds and tourist attractions to ourselves!
If Mother Earth is indeed going to get hotter ... opting for a small/short RV may make more and more comfort-in-all-conditions sense.