I've also found the large ziploc's aren't airtight either. I purged the air out of them before sealing them, and in a couple days they are puffed up with air....Doens't sound air tight to me.

I bought a vinyl airtight bag from ebay for 20 bucks. I was a little upset when I got it though.....It stinks like vinyl really, really bad. I've got it hanging outside airing out now, and it's getting better.