Not to speak for Mike, but car covers to me have limited applicability for cars that are outside. Usually you get one of the thick felty covers so that the car is protected from hail or door dings or branches, etc. One, the car has to be clean when you put the cover on, because not only are you risking marring the car, but if you get the inside of the cover dirty, then you are even risking it when you put it on a clean car. The covers get wet and stay wet for a while if there is rain/snow, and what do you do with a wet cover if you want to drive the car? It's dirty and wet, it's too big to put in your washing machine, etc.
There are the thin covers that are washable, but they don't give you mechanical protection. For me the best application for covers is in the garage when the car is clean to keep dust off. That being said, I did have a car outside for years with an Evolution cover on it, and that was better than it getting bird crap etc. on it, but there was always a layer of silt on the car when I took it off. That was one or two Evolution generations ago, so they may be better now.
Make sure you get a breathable cover if it is going to stay on there for any length of time or you will be sorry.