I hope that you can hear my sarcasm and don’t actually think that getting mold on your car is a good thing, but that is exactly what some people are asking for when they put a car under a normal cover for the long term.  What they should be doing is putting it under one of those waterproof car covers.  That way, moisture doesn’t even get on their hood or roof so there is no chance of mold accumulating.

You see, mold can form on normal car covers when there is a lot of moisture trapped underneath the cover.  The sun then increases the temperature significantly, making it a breeding ground for mold.  Going water proof will eliminate the water seepage and make it so you can safely leave a car under a waterproof cover for an extended period of time.