I installed my handheld Garmin GPS III into my SC. The GPS III contains only the general basemap and can't be supplemented with additional more detailed maps. I might move to a GPS V later.
I built a bracket out of sheet metal, primered it and painted it black. I bought a remote amplified antenna with a 15 foot cord and routed it under carpet and panels to the rear deck. I bought a cig lighter adapter, cut the lighter end off and connnected it into existing wiring.
Antenna: $20
Cig lighter adapter: $9
http://www.gpsgeek.com
It also works as a speedometer. Handy when you still have the old 85 MPH type:
My wife took this photo.
-Brad