When I drove my folks conversion van for a while, I too had noticed the dog house getting very hot... small block 350 crammed in there without much breathing room I guess.
never bothered to do anything about it, other than put the vents on "floor" and turn down the temp.
seemed to only happen at highway speed, that big bus didn't like doing 70-75+ mph on the expressway.
2013 KZ Sportsmen Classic 200, 20 ft TT
2020 RAM 1500, 5.7 4x4, 8 speed