I used to put together police cars by trade and i always drilled a 3/4" hole in the roof and used a grommet with little fingers in it and have NEVER had one leak, and put a good silicone to seal it all up. Run the wires in loom through the hole (put some silicone in loom at hole to) and it wont look bad. BTW silicone does not eat up sheet metal i have used it for years with no problems