Try to make sure the car cover you use is water repellent. Some of the cheaper car covers just soak the water up and let it get to your car's surface.
They make water repellent car covers with downward facing vents to promote air flow to some extent as well. Nothing too fancy, but could reduce or eliminate chances of surface rust forming, etc...

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2006 BMW M5 "Heidi" @ 109,000 miles
2005 MBZ C55 AMG "Lorelai" @ 165,000 miles
1991 MBZ 300E "Benzachino II" @ 165,000 miles
1990 MBZ 500SL "Shoshanna" @ 118,000 miles

(On the hunt for a good used M103 engine as of 6/10/23, PM me if you have one to sell!)