My car has a similar problem and I was thinking of a solution using magnetic sheets. My hardware store sells some to be used to cover duct registers. I was thinking of laying them over the edge of the sunroof and taping down the part over the glass and leaving the other half over the metal. I’m wondering if the magnet would be strong enough to stay on the roof. You see the magnetic signs on the doors of cars and they seem to stay there okay. I’m thinking that the tape residue would be easier to clean on the glass than on the metal.
Hmm… you might have something there! If you got a big enough one (like the blank white ones they use sometimes to cover up logos on trucks) it might just cover the entire sunroof and still have enough covering the metal roof to stay on without tape.
I do not think that the magnet is strong enough on the ones you are talking about to stand up to 65MPH wind. The ones that GreasyJack is talking about are designed for that application, so they should work. If you have a friend with some magnetic signs for the side of his truck, maybe he has some old ones with bad paint that you could try. I would NOT “borrow” one from the HVAC fellow down the road! He may not understand.
IME, those ones for covering house heating ducts do not work well for their intended purposes, so I would not try those at all, However, they are cheep & loosing one would not be a big deal, unless they flew off & damaged another car.
Just go to a sign maker or printer, tell them of the plan, and get a price quote.