I suspect that many (most?) tins leak after a year or so. Evidence: When I store tins in a box, I get that tasty aroma when I open the box, though the tins are sealed. So I use a pants and suspenders approach to storing tins -- i.e., leave 'em sealed and keep them in a sealed plastic freezer bag in a dark, cool corner in the basement. And don't mix types of tobacco in the same freezer bag. Another option: Some of those sealable plastic leftover food containers come in large enough sizes to accommodate several tins.