Many years ago, I used a tupperware container to keep a few cigars. Not for decades, but from one month to the next, or even a couple of months. It was OK for short term and think that if you are keeping an opened tin in a tupperware container for a while to prevent the tobacco from drying out, it should be OK. For long term storage I'd stick with glass. Whether the seal on the mason jars is rubber or silicone, so little of it is exposed to the tobacco that it does not matter. If you want to avoid glass for some reason, some folks have good success with mylar bags for keeping tobacco.