maybe So Cal has a bit do do with it too.
Local climate has a lot to do with it. I don't have any real idea what conditions are like in Alabama, I've only been there once and it was 30 years ago and only long enough to drive across the state.
In my area we are famous for our rain. Its not as bad as you hear, but moisture is a very real problem.
I would never wrap anything in a tarp because it does hold the moisture in and quickly leads to problems. I make sure things are far enough off the ground for air to flow under them, and I place some kind of barrier between them and the ground.
I currently have a cab setting out back. Directly on the ground are a couple of pressure treated four by fours. On top the four by fours is a 70's car hood which allows rain to run off to the ground, and keeps moisture from coming out of the ground into the cab. Then the cab is simply sitting on that hood.
This approach has worked pretty well for me, and I don't usually cover something stored that way. It would ideally be under a roof, but never wrapped in anything that would retain moisture.
I do put the things I care most about in my shop under a roof over a concrete floor. But shop space is finite...
