So you guys are saying that the C & D tins are as prone to leaks than the Dunhill type tins?
With the exception of cutter top tins, which went out of use in the 1970's, all tins are a hit or miss proposition for long term storage. The worst are the square or rectangular tins. Round tins are better. The C&D type tins can hold up, but it can vary with how the tin was made.
As an example, I opened two tins of Haddo's Delight, one from August 2001, the other from Jam 2002. The 2001 tin, which had a gold colored surface, was fine. The 2002 tin, which had a silver colored surface was dried out, stale. and a corpse. The interior of the 2002 tin had completely corroded inside, under the label, while the 2001 tin was perfect. While the tins looked identical on the outside, and in both cases looked perfectly fine with no corrosion showing on the outside, they were clearly of different manufacture, and were complete opposites in terms of maintaining a seal.
If you don't think your tins are leaking, try putting them in a sealed tupperware container for a couple of months, or less, then pop the top and take a sniff. Assuming you have a sense of smell, you'll smell tobacco, even though all of the tins are unopened.
Keep in mind that these tins weren't designed with the intention that they would need to hold up for decades. Long term cellaring is a recent phenomenon. But you can be reasonably confident for a few years before some tins start to fail, while other continue to hold up for a longer time.
Finally, if you can't provide a cool, dark, dry place to store your stash, that's your problem, because that's your part of the long term storage equation.