Another method I found, which hasn't been thoroughly tested, is to get a large bucket, fill it with rock salt. When the salt becomes fully saturated lay it out on a tarp in the sun to dry it back out. The amount of rocksalt you use will infuence the amount of time between dryings, and if you want to speed of the rate of dehumidifying then have airflow through the salt or increase the surface exposure of the salt.