I use a Carcoon for my Seven which is kept in an cold and damp garage. It's a bit pricey but works very well, stops all those problems caused by damp - corrosion, grabbing brakes, gremlins in the electrics etc etc. I can certainly recommend it as I could see my car going rusty even as I was building it! Now damp is nothing like the problem it was before. Helps keep it clean as well.
Cheers
Ezzer