The questions really has to go hand-in-hand with whether or not you have shore power available. You're extremely limited without it, as any form of desiccant simply isn't enough. In our first TT, we had several canisters of Damp Rid, and it would solidify the crystals in a few days, leaving it totally useless.
We have shore power and use a large stand-up dehumidifier. We leave the AC at about 80 degrees, which helps a lot when it's running. But without the AC, the dehumidifer will take out about a 1/2 gallon to 1 gallon a day to keep it at 40% RH. On the bright side, it never smells musty or moldy in our camper.
