This is one of those things that your mileage is definitely going to vary on, but I thought I would pass this on. I cleaned out the back of my Jeep today and found a small Mason jar with maybe 3 or 4 bowls worth of tobacco in it. I couldn't remember what it was--it smelled like latakia--but it had been back there for a long time. It was really dry. Just crackling dry. So I thought I'd go ahead and see if I could revive it enough to smoke.
This is what I do to moisten tobacco: I put fairly small quantities of it in a small Mason jar in a sort of ring so I can put a small medicine cup upside down in the center. I fold some tissue paper (take your pick, although I'd suggest not using anything that's been scented or lotioned) into a small square and wet it, then squeeze out pretty much all the excess water so that it's quite wet but not dripping. I put that little square on top of the medicine cup and put the lid back on the jar. Let it sit overnight or longer, depending on how much you want to moisten the tobacco. Don't let it go too long or it will start forming mold. Where I live, the one time this happened to me it took several days (one of my experiments).
It turns out that after a night of my moistening treatment, the tobacco is quite smokeable again and turns out to be some of C&D's Mountain Camp.