Not to make light of the problem, but I did smile when I read the postings and then went back and reviewed where the OP and the subsequent posts call home. No one, with the exception possibly of the folks from Florida, live in a really hot area of the country like those of us in the Southwest. Here in Oklahoma, going down the road in July or August often sees an ambient temperature of over a hundred so you can only imagine how hot that truck chassis (yes, it is a truck) is getting from the engine and exhaust system including the converter. The highways get easily measure in the 120-30% range on days like that.
Therefore, I must say I never even noticed the heat in our PC. My wife never mentioned it. Having had several Class B and Class C motorhomes over the decades, maybe we are just use to the fact they get hot and sometimes REAL hot. You might want to make doggone sure that the doghouse is properly cinched up and the seals on it are all in contact with their setting. Also, you cab use this under the floormats:
http://www.lowes.com/ProductDisplay?partNumber=13357-56291-BP24025&langId=-1&storeId=10151&productId=3011904&catalogId=10051&cmRelshp=req&rel=nofollow&cId=PDIO1If you read the reviews, you will see that the trailer guys and Class B folks cut out inserts from this stuff for their windows to keep them cooler and it works for that as well. I made a set for each window in our previous RV and carried them with us for when we were camped in the summer sun.
Under the floor mats, simply cut it to be that same size and layout. Then, you can use carpet tape (double sided and extremely "sticky") on both sides of the Reflectix to hold it to the mats and floor. Incidentally, the tape can also be used to keep those pesky mats by themselves from slipping around like they are prone to move.
Please don't think I am deriding the problem of the heat for my fellow PCers.....it is just that I am so adjusted to a lifetime of HOT HOT HOT that I am not cognizant of or sensitive to some of these things.
Paul