we live in the south (Alabama) and the heat from the engine that comes up to the back of your butt is really hot. Go through some water when it is hot and you are very uncomfortable.
The rubber thing mounted on the rear bottom of the cargo bed is NOT SUFFICANT.
My answer was to use 2 swimming pool foam noodles cut and placed between the bottom seat and the back rests. It helps but does not cure this problem.
Other people have had this problem. I have heard of people mounting a piece of metal to block the heat. Other people have used insulating foam (not sure if that is better than the pool noodles you used.)
Maybe try using the search bar to see what you can find.
mount a 10 inch fan passenger side front of seat that will blow back. across headers also ceramic coat headers and shields then get rubber sheet recall kit and add windshield sun visor cover under the top of seat I also did a complete thermal wrap around bottom and back of seat