I also have an E-450 based class C that had a very hot floor and engine doghouse. It was a problem for our little dog who liked to curl up on the floor in front of the passenger space. I removed the doghouse (fairly easy to do - 4 clips, and then out) and inspected the limited woven insulation installed at the factory.
I bought some DynaMat heat/sound insulation from Best Buy near me. This stuff is often used when installing upscale sound systems in cars. It is two layers of aluminum foil with a layer of black mastic between them. Only about 1/8 to 1/4" thick. One side has a self adhesive film which is exposed by removing a thin pull-off sheet. It cuts easily with scissors and sticks very firmly to the plastic doghouse inside surface. I reapplied the original factory insulation over the DynaMat.
The work really reduces the heat transfer through the doghouse. Now I will turn my attention to the floor heat - have not done so yet. DynaMat, or other similar materials are not cheap - they run about $5 to $10 a square foot but they do work.