Don't use table salt, but definitely salt it! Buy coarse pickling salt in bulk. We used to do this all the time when we had to bring the hay in from the field in a hurry. Lay a row, salt it, lay another row, salt it, etc. If it must be covered, try to have the ends open so the wind can go through. I put 125 bales of damp hay in my barn two months ago and it is as dry as can be now. The first two weeks I left the loft door open because you could feel the humidity and heat in the hayloft after the first day, but now it's beautiful and the horses love it!