humidity,,,, almost as vile an enemy as gravity to us older folk.
marine stores sell a product that basicly absorbs moisture from the air.
not sure what its made of , silica or something. you put a package or two in the cabin and it keeps from getting that nasty moldy boat smell.
should work in trailers too,,and as i recall was only a few dollars. certainly not more then ten or i would have been too cheap to buy it.