I had a problem with moisture under the mattress of the cabover bunk in my Class C motorhome. I needed something that would allow air to circulate between the mattress and the bunk bottom. My solution was to install a material called Easy Tile 12-inch by 12-inch Dry Floor Interlocking Drainage Tiles over the complete bunk bottom area (I used 28 tiles). Since then no moisture has been detected. The tiles are 7⁄16-inch thick and have ample air space. They come in boxes of 10 tiles at about $25 per box and are available online and at Ace Hardware.
Keith Johnson, Bow, Washington