You can buy silica gel at a crafts store, I bought some to do the same
job as you are trying to do.It is used for drying flowers to preserve
them.You will pay more at a tool supply for the same product.The craft
store price is a whole lot cheaper for the same product.The product is
loose in the package,I put some in brown craft paper like the ones from
the supermarket shopping bags.Cut the paper into a small packet and
staple it closed.This paper is porous enough to absorb any moisture in
your toolbox.Works great.