Thanks for your post. I enjoy seeing those really old tins and tobacco.To the OP: well, I went to look for some old tins to show. These first 4 pics all have tins older than 20 years. As you can see, all look like new, storing them in boxes like I explained elsewhere.
Some of the following tins may not be as old, but they are all from before 2010. I tried to pick different types of packaging to show how they all fare.
Finally, here are the Peretti cans, over 20 years old. They are of Somerset Slices, and the bottom one is a pic of it as I am smoking today (sorry, there's only a little left).
As you can see, no problem storing old tins. Good luck.