In most garages the floor is the first place to collect condensation. The problem when using an ordinary car cover is that as the moisture starts to dry, it’s allowed to rise up into the vehicle. It can then become trapped under the cover itself.
Most manufacturers of ordinary car covers have considered this problem, and claim that their cover will breathe and let the moisture pass through. The fact is, if the cover didn’t let the moisture through, it would have serious implications. As it is, moisture is very slowly passing through the cover, and this now-damp cover is resting directly on the vehicle.