The warranty on mine, both 2 year & 5 year structural, are over with, but it still has the sticker next to the door stating it's a residential rv.
Some, if not most, insurance companies won't cover them if fulltiming, that's why we're on an extended vacation in ours.

National General specializes in Full Time. I don't know that they are the least expensive though...

In the last year and a half since going fulltime we have been in everything from a below zero, 40-50 mph wind blizzard to 110 degrees here in AZ. The coach has done very well and am very happy with it.

Lots of good ideas and fixes listed here.
When it is hot with direct sun, we keep the shades closed to help with the heat.
With all the A/C mods I have made to improve the air flow and performance of our A/C units along with heavily insulating the front cap area we are able to maintain mid to upper 70s inside in 100 degree heat with 2 A/C units.