Finally fitted my rear camera for my Mi-Witness dash cam.
I bought and fitted the cameras to my Mark 6 Golf originally. It was a nice easy job, the fuse box was easily accessible (simply remove the cover on the end of the dashboard on the driver's side), and no real problems running the wires. I did the whole job in about an hour and a half.
The Mark 7 seems to have been designed to make simple jobs impossible. From the location of the fuse box through to the near impossibility of running the cable for the rear camera, and tucking it away out of sight, the interior seems to conspire against you at every step, unless you take out the rear seat and the trim panel below the rear side window (it's a 3-door).
I managed it eventually, but it's not a job that I would volunteer to do again.