I have tried various things also and none of them make much difference. Finishes just don't last forever. The things that seems to work better than most is keeping the container in a cool air conditioned location in the summer and not let it freeze in cold weather. I have kept finishes for five years or more without any noticeable problems.
I think that the biggest problem with cans is not getting the rim perfectly clean before resealing it. Also, a dented rim can't seal. I am very careful about keeping the rim in pristine condition and cleaning every last bit of finish out of the groove. All that and NEVER hit the rim with a hammer to reseal the can. If you have to use a hammer, that is a clue that there is a problem and hammering is making it worse. A rubber mallet can be used, but just be careful and don't compensate for the difference between rubber and steel by flailing away at the paint can.
Your food tubes reminded me of one backpacking trip many years ago when I got the bright idea of putting some stuff like peanut butter and jam and cheese spread -- just in case anyone doesn't know about the air pressure difference between the flatlands (about 600 feet ASL where I live) and the mountains where we backpacked (about 9500 feet ASL), it took quite a bit of work to clean all of that stuff from the inside of my backpack. On top of that, the pack was crammed pretty tight and all of the bouncing across boulders combined with the pressure inside the tubes was more than the little clip seals could take.
Last edited by Bill Boehme; 03-23-2014 at 11:03 AM.