John,
An 'on the glass' antenna should work for you. Mounting
an antenna on the Fiero's body will also work but will be a
real P.I.T.A. since you will have to make connection to the
underlying metal (it's there, just very hard to get to). So,
unless you want to go to a huge amount of trouble for very
little benefit, use the 'on glass' antenna for VHF/UHF. If
you want HF, you will have to start thinking about making a
making a mounting bracket that connects to the car's 'frame'.
Not easy, pretty, and an even bigger P.I.T.A.!
'Doc