Wild idea -- skirts & a propane flame box underneath?

I was also tossing around the idea of the skirt around my class B in another forum. No propane heater involved, though. It would probably help for a few degrees below freezing. Some responded that if it's warm under there, and closed off, some critters might decide to call it home. A little while before we had a family of skunks pay us a visit in the middle of the night. With a skirt around the RV, they might have become neighbors.
As others have said, I would stay away from any combustion source.