You could actually bury the antenna in the roof header if the roof is all fiberglass, as it won't block the signal as much as a metal roof will. You could leave a piece of sheet metal stuck to the magnet antenna, but I would bury it INSIDE the car with a chunk of metal under it. Should work pretty decet that way, especially if your city has terrestrial repeaters.
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You could actually bury the antenna in the roof header if the roof is all fiberglass, as it won't block the signal as much as a metal roof will. You could leave a piece of sheet metal stuck to the magnet antenna, but I would bury it INSIDE the car with a chunk of metal under it. Should work pretty decet that way, especially if your city has terrestrial repeaters.