I would go the charcoal route. My featherweight case smelled horribly of mold. Tried everything -- sunlight, heat, soap, softener sheets. Nothing got rid of the smell. Then I bought a pair of OdorEaters charcoal shoe inserts and put them in the case with the machine. After two weeks, no more odor! Ever! (The OdorEaters provide some nice cushioning in the case, so I just keep them in there permanently now.)
Charcoal is one of the best for actually absorbing odors instead of masking them. On Amazon you can buy something like this:
http://www.amazon.com/Pack-Bamboo-Ch...pr_product_top