Several years ago, when I had more cars than I had storage, I had to put some of them in a damp underground garage. I knew there would be a moisture problem, so I looked into what my alternatives were. I ended up covering each car with a cheap thin car cover, and then rolling them into these large plastic bags. The people I bought them from said they were for car storage, but I found later they were originally meant for outdoor grain storage. It took a little effort (the more help you have the better) to get the cars positioned right, but after I got them where I wanted them, I placed a tray of desiccant under each car, and used my shop vac to suck as much air out of the bag as possible before sealing them up. When I removed the cars from the bags the next spring, everything was perfect; no rust, no mold, nothing. They were like the day I rolled them in.
I did the same thing the next winter. That spring, while the results were still OK, they weren't as good as the first year. It turns out that moving the cars in and out and folding them up to store them over the summer caused some pinholes in the bags, so they wouldn't seal perfectly on the second use. They were only about $90 each as I remember, so they were a good one year solution. If you have to do it subsequent years, I would suggest buying new bags every year; 90 bucks ain't that much. I never tried it, but I would expect the results would be good if you left the car in the bag for several years if it weren't disturbed.
Just another alternative.
