You're trying to hard =) There are two things you need to worry about when installing your GPS antenna.
1) There isnt any metal over it
2) It is sitting on grounded metal

Since the thing is magnetized, and since 99% of the metal in the car is grounded... all I did was feed it into the drivers footwell area, then just felt around with it in my hand until I found a nice metal surface for it to stick to.
Then I just tied the wire out of sight. Done.