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The reason you use Mylar when packing long term storage is it is virtually impenetrable by oxygen. Plastic even that used in vacuum bags allows oxygen in over time.

[Kartographer]

You can shop around and get the bags at a good price, but the shipping takes a bite. If you can the Mormon cannery at a very fair price. Try to get yourself an invite. The rules very and most of time you need a Mormon ‘sponsor’ to go with you and you get one visit, but I encourage you to go. My was a very good experience with no pressure and lots of fun and camaraderie.