We have a rear kitchen KZ TT and installed a Garmin backup camera. Absolutely no spot on the rear wall to mount it and penetrate the wall for the cable. I made a bracket/stand for it to sit on the bumper. Easy since I have a MIG welder tho. Could probably do with some wood and paint it black.
I ran the cable from the bumper to under where the pantry is and where there was already some wire routed up a hole in the floor. I peeled away the luan on the inside of the pantry to gain access to the wall cavity (adjacent to counter) and ran the wire up into the ceiling space. Interestingly, the Garmin cable from the camera is only a few feet long and ends up outside and the connector/plug is not water proof so had to use some heat shrink tubing on it.
I ran the cable all the way from the rear of our TT to the cabinet above the bed via the ceiling cavity. To do this, take down speakers, AC trim, skylight trim, etc. to gain access to the cavity. If you have the older type pancake style lights, you can enlarge the hole behind it. Use a fish tape to get the wire between access points. Sometimes a slightly bent wire coat hanger helps to get around some obstacles. May take some patience to get it done.
Note that you will need a positive power source off the 7-pin connector at the TV for power when backing up. At least that's what our Garmin needed otherwise the GPS screen would not display and would always been in backup camera mode. Also, the camera doesn't need to be up high.
For all the work and expense to install the camera, I can't say I'm in love with it. Most of the time DW is with me and she spots for me when I need to back up. The image on the screen isn't all that clear but does work well enough - just. I have yet to fiddle with the transmitter above the bed to see if that does anything. Every once in a while, the camera image won't appear on the screen for some reason. Not sure if it's an issue in the truck, the 7-pin connector or something else.
Perhaps before you go to all the effort to route the wiring through the trailer somehow, do a mockup and lay the wiring on the ground and see how the image looks.
