Both above are good suggestions. I've used a Noah cover from Wolf as well as a cover from Coverking recently. The Coverking one was less than $100 (from National Parts Depot for a '67 Camaro); had it a month so far and works great!
you get what you pay for in this instance. The race car is in the garage so my car is in the driveway.
I have one of their thick bad weather covers (I dont rember the nma) on my car for almost 4 years...snow, rain, hurricane Sandy, sun... Car always looks great underneath. Not effected by acid rain or bird poop. It is thick enough that the occasional careless bump from family members or the kids friends (ie plastic garbage or bicycle grips) protect it.