Hi Cheshire Cat,
Yes and Yes...thank you! The cable enters the tube from the body with the rest of the loom and rear washer supply tube but exits a few mm from the loom outlet at the other end, but well within the boundaries of the grommet, so it's sealed.
I pulled the concertina tube from the body and the bottom of the back door. I pushed/manipulated a wire probe ( thin coat hanger wire with one end bent a full 180deg backwards 10mm from the end so that it presented a smooth surface to push through the tube) from the vehicle body end through the concertina tube until it was pushing firmly against a "soft" wall section of the grommet housing adjacent to the loom "outlet". I was then able to carefully probe that area of external wall with an "exacto" / scalpel blade until I felt it cutting against the wire probe... this way I was able to be sure I wasn't cutting into the wiring loom inside. I enlarged the cut and pulled the wire through.
I put a couple of short squirts of silicon dry lube into the tube from both ends.
I reinserted the wire probe -rounded end first- and manipulated it back in the opposite direction , attached the coax connector to the rounded head with cloth tape in such a way that there were no sharp edges. I then slowly pulled the wire probe back through the tube manipulating it to clear the wiring loom and rear windscreen washer supply tube. The silicon spray was amazing and the coax connector virtually slid through the cable and popped out through the small slit previously made with the exacto blade! I was then able to pull the coax freely either in either direction. I pulled a sufficient length of cable (plus a bit!) through the tube to position the camera, then fed the wire probe up through the hole in the bottom of the door to draw the cable though. With a little spray around the edges of each grommet end, they popped back into place.
I sheathed the cable in the door with 7mm split conduit ("loom tube"). I'd noted the advice elsewhere here and purchased an optional 10m coax. I'll gather the excess, bind it and stow it under the panel covering the wheel arches. Tomorrow I'll reassemble the interior....
I have no garage access at the moment. I am working on the vehicle in sunny Queensland weather while it is parked across my driveway. Our narrow street is about 200m long with only one entry/exit. The neighbours on their daily walks are bemused that I would pull the panels out of a brand new vehicle...
and do I know where all the bits go when I reassemble it? I explain that it was designed to be "adapted"...
I do not intend to make a living as an accessories fitter