Making A Warmer Truck Camper Bed

It seems hard to believe but the area under my mattress was just a raw piece of plywood. I sealed that with a couple of coats of enamel paint so no moisture soaks into the wood. For normal Summer use, I occasionally check but there is never any moisture under the mattress. When the outside temps are cold, around 40 degrees or below, I need to raise up the mattress with a foot stool and then use my 12 volt fan to dry the area. I do that once or twice a week before any serious dampness accumulates.

There are pads that can be used to keep the area dry but I don't want any increase in thickness because the ceiling space over the bed is already minimal.