Under The Mattress Mold

I have an R-Pod 178. 

I've been having an issue with mold building up under the mattress and on the warm side of the plywood bed frame in my R-Pod. This even happens when the weather is warm and dry outside. 

I'm assuming this is simply condensation build up from my body heat keeping the mattress side warm, and the cooler air being under the plywood bed frame (half the frame is over the rear unheated storage area of the R-Pod).

Has anyone had a similar problem, and how did you fix it?

I'm thinking about putting a Styrofoam sheet down under the mattress to help insulate the mattress inside from the cooler temps from the storage area. 

Any ideas?

Thanks in advance