I put one on the back of my 24' trailer which is towed by the 31' motorhome. I ran the cable up to the front and bought a Magellan gps that had a big 7" screen that would also accept video in. The video in on the GPS used a different ring of the input plug than normal, but that was probably to make sure that only 'their' cords would work. Just buy an apple 4 ring plug that adapts to several RCA connectors. Find the one that works, it's that simple.
Anyway, next I put a switch to send some 12v to the camera in back. Now, when I flip that switch, the camera in back of the trailer appears on the GPS screen. I can also see the back of the motorhome, since that 3 camera system was untouched.
To make things even more complicated, since I like to tinker, I added a camera inside the trailer, with infrared lighting, to watch the fragile load, which is very close to the edges of the trailer. That also has a dedicated switch, so that it will also interrupt the gps screen when I flip the switch, and show up on that nice 7" screen. GPS continues to work, with voice commands, during this. I think the model was a 170 Magellan (not sure), and it has it's quirks, but was pretty cheap, a hundred and something.
Dual camera kit with quick release plugs was gotten from Ebay, and I'm sure it's Chinese, but it works so far. It came with a coily cord to go between trailer and back of RV.
I wire tied the cable along the bottom of the frame, tucking it away from harm's way whenever possible, and ran it up through a rubber plug in the driver's area, that was very pliable and easy to fish the line through. Then just added an extra fused output for the switches.
I like it, and for a couple or 3 hundred bucks or so, why not? More information is better, especially when the transmission is in reverse.
Coachmen Pursuit 31BDP 2013, 300w solar, 1200w sine inverter, In-motion Winegard Dome sat. ant., L.E.D. lights, P2 brake controller, Yamaha 250 on back carrier, or pulling Stehl dolly with Hyundai Santa Fe