Now that you've run the reverse backup camera, there are some things that need to be done in the front trunk. I mounted the GPS antenna under the plastic cowl where the windshield wipers are. This gives good access to GPS antenna but protects it from the rain. The GPS signal will go right through the plastic. Here is a picture of where I mounted it (left of the battery).
The second thing that you'll want to do in the front trunk is run the wire for the Vehicle Speed Sensor (VSS). This is a signal that varies based on your speed. You don't really need to run this since it is only used to approximate where you are if you are in a tunnel, but my receiver had an input for it and I ran it. This is the white/brown wire in the big thick wiring harness running to the controller on the right front of the front trunk. There are two wires here: a mostly brown one that has some white and a white one that has a little brown. You want the mostly white one. The big control unit cable bundle goes through the front trunk compartment so tap into it near the battery:
You'll need to get these two wires through the front trunk compartment into the cockpit of the car. This is easy. There is a big rubber grommet to the right of the battery (looking from the front) and you can cut a slice in it and run the wires through. I'd loosen the battery and move it to the left to make it easier to see:
Next, wiring up the dash.