where to install a sirius satellite antenna

[boonie]

on my 94 C4 where in the world can i install a sirius satellite antenna? ive been told that you must have a metal ground to recieve a clear satellite signal, so whats a guy with a fiberglass body suppose to do? has anyone dealt with this problem?
thanks boonie

 

[Magmotor]

Did the instructions say that from the center of the antenna, 6" of metal must be surrounding it?