Here is what I do guys.
I buy two car covers once a year at walmart. I like getting the dupont tyvex material ones. They are very waterproof for about a year, then you throw them out.
You roll the car onto the one cover, and tuck the other cover over it, then rope the two together.
Car stays dry, and when spring comes you just throw the car covers out.
The car covers are 19 bucks each i think.
Those shelters sound like a good idea, until the first blizzard comes along and the thing falls over.