Winter's coming. Rust prevention?

I've seen a few ideas out there to prevent rust in classic cars. From the inflatable car bubble, to a zip-up car bag with large silica sachets inside, but what a pain come Sunday when it's time to get it out for a spin. If the car is to be parked on unsealed concrete that can allow water & moisture to pass through the slab, is it a good idea to lay down a tarp beneath where the car is parked? Or will the tarp draw more moisture through and add to a damp environment?