i dissasembled the gameboy to paint it beforehand
parts involved: a stripped down usb gps and simple plastic enclosure
also half of a game boy data cable. my gps directly had the data + - of the usb circuit outputing nmea serial data, so it was easy to wire this in directly. power came from on board AA's
attached to the back via velcro. the enclosure might be a bit thick as it lowers the signal from gps, but overall it works fine.