We had the same problem with our new Greyhawk FS 2014. My wife complained on the way home from the dealership. I had a local audio shop install Hushmat in the doghouse. It dramatically reduced the noise and heat. The floor is still too hot but that is harder to fix. You can put lizard skin on the underside of the chassis however you need to paint it. I am also considering installing heat shield around and headers. That should also help.
2004 Chevrolet Silverado 3500 LT with a 2004 Jayco JayFlight 29BHS
2014 Greyhawk 31FS with a 2007 Tahoe toad
2014 Thor Palazzo 33.3 with a 2007 Tahoe toad