If you have not already - spend some time here, researching posts:
FROG - Forest River Owners GroupAlso, drill into the Forestor section (basically sister model to the sunseekers).
There have been posts about AC and insulation not being the greatest on some of the Sunseekers. SOme discussions on adding a secong unit to larger Class C's.
I know with extreme heat, it is necessary to completly block off sunlights, windows, etc, along with running a fan to move air... To maximize cooling efforts.
I have a smaller Sunseeker 2960s (single Slide, small), 28.5 foot Class C. 2014 model, have owned it year & half. No major issues with our model, pleased with the rig so far, some small issues, couple warranty items handled well by Forest River.
Good luck with your search.
Markiemark:C