FWIW, I once stored all my books in a barn for a year without ill effect. I put them in small boxes and then wrapped the boxes completely in plastic and sealed them with tape. There was no mold or mildew when I unpacked them a year later. On the other hand, the barn was above ground and was basically dry. I was more worried about insects than damp or mildew.
I think the idea of dessicants is a good one.
Roddy