This is fantastic! Awesome write up. I will be doing this soon. One thing I would like to try is adding an analog video switcher such as this. The reason is so I could have the exterior rear trailer cam and the 2 interior, cams and switch the source accordingly for the interior cams in the single interior cam port on the bumper. Of course I would need the DVB-TV to RCA for the splitter. One reason I think this might not work is the GM cameras seem to get power and video line all on the single DVB-T to Fakra A cable. If i were to add a splitter inline it may kill the feed entirely as the power might not pass through as expected. None the less, the switcher is cheap enough and so would the adapter cables to test.
On another not I plan to design a 3d Printed mount for the cameras. I can provide the .stl files once I figure it all out.
Again thanks for the write up.