The cave sounds nice. Here in Texas, if there is a cave, it is either hidden away and used as a bong shelter, or otherwise not mentioned.
If a cave were available to me, I'd buy some large, plastic trash cans, and put some large Damp Rid containers in them. I always put the calcium chloride in another container because of its innate caustic nature. Alternatively, some "Driveway Heat" (pellets of calcium chloride, comes in 50 pound bags) in a trash can might be a way to ensure humidity is kept out of the air as well.
Here in Texas, the best solution is a pole barn or aluminum carport. A friend of mine made a box out of air filters that sits on top of his roof vent while his rig is in storage, and he runs the vent fan backwards, sucking in air from the top though the filter box. This not just keeps the air moving, but because of the positive pressure, bugs don't fly in.
