Great tutorial. I did my rear cam before I read this and realise I was lucky not frying anything as I neglected the battery disconnect step. LET THAT BE A LESSON TO
YOU 
I also picked up some other clues thanks.
From my experience and other posts I would like to share that :
leads exiting the 'plate light thing can go out one of the light holder holes. The holders seal against the metal with foam that is thick enough to absorb the wires. This avoids messing with grommets.
If keen, cover the holes the lights shine down through with colorless plastic to keep dust out, AND refit the light thing with a bead of silicone around the edge where it contacts the metal. Smear the contact area of the metal with petroleum jelly first. Allow the si rubber to skin before driving or dust will stick to it. Doing all this prevents that wet dirt that comes down after you have washed the car.
if feeding thru the conduit between the trunk/boot lid and body you can make slippery inside with silicone spray and also compress/concertina the corrugations, insert the connector as far as possible, pinch it to keep in place, relax your compressed part, repeat etc etc.
rather than along the door sill, the leads can most easily be fed from the trunk/boot between the backs of the rear seats then tucked up under and along the center plastic console edge to under the dash. You can lift the cushion of one seat out to see what u r doing. (Undo the bolt, push the cushion back and press the back of it down to separate a metal loop on the cushion from a hook on the body. Collect all sorts of goodies you may find.