Cooling Issues in my stealth camper

Being from California I'm not much of a mold expert. But I have spent significant time in south Texas and San Juan building studio facilities, and once moisture, almost any moisture, gets into drywall, black mold can follow at the speed of light. Once it's in the rock, it's in the rock. Sometimes you can treat it, other times it's a demo. The last thing I personally would use is porous rock in a trailer of any kind of RV that has a better than 50% chance of water intrusion at some point. I would use Luan or thin paneling and moisture seal it... Lighter, easier to install, no cracking (another guarantee), and a better insulator than a piece of rock.