IMO, I think if you're garaging it you're better off not covering it. At that point a cover really isn't doing anything but telling your neighbors you're super anal. Plus I had a bad experience one time when rain water leaked into the garage and I had the car covered- the cover trapped the humidity and held condensated water against the sheetmetal for a solid week before I discovered it.
That was in a garage that was literally 100 years old and did not do well with humidity and temperature changes, so I'm sure you wouldn't have the same experience in a well-built garage. But after that, I just don't see the point. I tossed the cover the very next day. And fixed the rain leak, of course