I used a generic camera, monitor and wireless link off ebay.
The camera is mounted under the back of the caravan, I ran a double screened cable forwards and up into the front bed box, one cable for the video signal the other for 12v to camera. The transmitter is in the front bed box stuck to the body with double sided tape. 12V supply comes from the fridge supply so it is only on when car is attached and running.
Its suprising how much you can't see through your mirrors!
Initially I used a camera with built in wireless but the distance from back of caravan to car dashboard was too great.
Be very careful going wireless. I've had 2 and they were both useless. First one was a rear view mirror screen, the transmission was analogue and reception awfull. The second one I went for WiFi that hooked up to my smartphone screen, the picture kept freezing for seconds at a time, can you imagine a worse feature of a reversing camera!. Undeterred I'm going to fit a twin wired one this winter. You've got to run a power cable anyway so it's not any more bother to put in the signal cable.
For a reversing camera on a car I would not even consider wireless.
I used a wireless link between caravan and car. The camera is in effect a rear view mirror to see what is behind me. There is a 2.1M wide blind spot behind the caravan
Andy, is your camera permanently on then? Do you have a small screen in the car that acts as your rear view mirror, makes sense if that is what you are doing, may just do that myself,
regards
I have a 5" screen that fits to the windscreen with a sucker and gets its power from the cig lighter. the camera and wireless transmitter are powered from the caravan fridge supply. They power up when the caravan is attached to the car and the engine is running