GPS mounting
You can buy a little bracket, I think Edson makes them, that fits on the pedestal and is made for this purpose. As for the electrical, some drill a hole in the pedestal, and run the wiring through the tubing and under the cockpit. If you have an external antenna, you can't do this without cutting the antenna plug off and rewiring it. On my boat, I drilled a hole in the cockpit floor large enough to get the plug through, ran the wires through the hole. Then caulked them up really good, and installed a clamshell vent cover over this. Works good and is water tight.