Rice. Cheap white rice into me wife's old pantyhoses. It has worked as well as desicant paks or cat litter I use. VCI bags are great, but sizing for bulk ammo storage I've never found. Past this I can't find them in lots of like 100 or less and they get damned expensive in larger quantities which are the only ones I can find now. 44MAG used to sell them in small lots and several sizes, but they're gone and those I used almost all off them for vintage usgi mags I collected over the years. So rice in nylon.