Do you want the camera to be powered only when reverse is engaged or powered with ignition?
I installed a reverse camera powers on our MK1 which powers with ignition, I hard wired it to the fuse box. However I also installed a rear parking sensor on our MK1 which was powered by the reverse bulb.
All I did was splice a couple of cables onto the harness of one of the reverse lights. The camera uses very little power so it should be really be a problem, but to play it safe and to get a nicer more useable reverse light, I changed the reverse halogen bulbs for LED ones which consume less power to compensate for the power the camera uses.