I keep mine in a cigar humidor. It works like a charm. If you can't afford a nice one go to any cigar shop and get one of these babies. They range anywhere from 3$-10$ but they are so worth it.
They have a gel inside of them that absorbs like 300 times its weight in water and the gel slowly lets the water evaporate after it is absorbed in a way that keeps it at a perfect humidity level within whatever enclosure it is in. Grab one or two of those, fill them with water, toss them in a tupperware or plastic bag and there you go. Perfectly moist and preserved.