I agree that anything put on bare ground is liable to absorb moisture in the winter. I have my ducks run on bare ground, and their sleeping area is linoleum covered plywood. I use wood shavings in both areas and the ones in the house stay dry since I scoop poop everyday. I do the same in the run, but the bottom layer is always a little wet in the winter. I just try to not make it too deep, fluff it up regularly with a rake, and also scoop poops to keep it clean.