Winter storage for many of us is a fact of life it'd be interesting to hear what others are doing there. The best outside storage I found was to flip the boat over. I tried tarps but the never relenting wind here would flap the tarp no matter how well you tied it down and start to erode the gel coat. While they say its not enviromentally or economically friendly I'm jealous of the shrink wrapped cruisers. Now I keep my DS inside but even that isn't perfect, nothing a cat can't cure though.
I also have to admit to storing sailboats with no cover at all and not having any issues. However, as a sample of what can go wrong I have an old Crosby outboard that I've stored poorly for years and now I see the coring is bad and it's going to be a pain to repair if even possible.
Baysailer