How do you store your open tins?

I only smoke about once or twice per week. So my three open tins have been open since December and they're starting to get dry.

I like the idea of having about three tins going at the same time for some variety, but TOO dry of baccy is no fun.

How do you address this?

Right now I have them triple-ziplocked, but even at that they're getting a little too dry.