In the same way as I channeled my mother on mother's day, I am channeling my father on father's day.My dad was an excellent, if ferocious housekeeper -- dirt and disorder had no chance with him. He kept all his woolies in cardboard boxes, and in later years, in plastic snap top bins. Into each box or bin, he dropped a bar of scented soap--he strongly favored Zest. Until this day, that "Zest-y" smell takes me back to the odor emanating from his sweaters. And not only is this a good way to store woolen sweaters, it is also an excellent way to store yarn. Just pick a soap with a scent you won't tire of. (Hint: for a smaller storage bin, check out travel sized soaps.)
Whether it was the snap top bins, the soapy smell, or some combo of the two, my dad's woolies never, ever suffered from the dreaded m*th.
Addendum--an e-mail inquires whether the soap is to be unwrapped. The answer is "no." An unwrapped soap would shed little flakes of soap power into your woolies--a whitish dust which would be best to avoid. You simply drop the soap bar, still in its original packaging, into the woolies bin and seal the lid.
--TECHknitter