I've tested the "airtight" gamma lids for 5-gallon buckets. Though friends have used for years with no mold, etc., they have a relatively dry basement, so no big challenge. I put a hydrometer into a bucket, sealed it with a gamma lid (with collar in place and gasket checked), and took it outside overnight. The next morning, the hydrometer showed a big difference; it was no longer the 40% humidity in the house, but the 75% humidity from outside. So... that tells me, they are not airtight. They might be the best that's available, but the reality is.... The best option seems to be to seal a mylar bag, but how does one do that? That handwarmer oxygen remover doesn't last forever. How does a person seal a mylar bag? The only other option is to get a FoodSaver seal-a-meal machine that sucks the air out; I did that, too, but most of the sealed bags eventually leaked. Want to use mylar, if there's a RELIABLE way to seal.