I have been watching this thread with interest as I also have issues backing the car to hook up the van as it is mostly a solo effort on my part.  I have a camera to go into the number plate light but my GPS does not have AV in so would have to have a separate screen.
As I only need it when connecting up the van not for general use, and as I do not have AV - looking at the issue I am not going to do a permanent installation and going to buy a $50 wired system and using a couple of velcro dots connect the camera on the tow bar, lay the cable through the car over the seats and plug it in to the rear power socket for power, do the hookup to the van and then just unplug and store with the tow equipment until required for the next use.
The effort that you have gone through is just too much effort for my requirements.
Good luck with your install.
Cheers
Garry
				
			 
			
		 
			
				
			
			
				REMLR 243
2007 Range Rover Sport TDV6
1977 FC 101 
1976 Jaguar XJ12C
1973 Haflinger AP700
1971 Jaguar V12 E-Type Series 3 Roadster
1957 Series 1 88"
1957 Series 1 88" Station Wagon
			
			
		 
	
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