Ive been using these from Rubbermaid:
http://www.rubbermaid.com/en-US/easy-find-lids
The lids lock together and are stackable. I bought mine at http://www.ollies.us/home.html but was recently in Costco and they had a killer deal on them.
Maybe I'm overlooking someones response, however, I don't see any mention of using a vapor barrier. You'll want to add the vapor barrier to help with the mold and mildew.