I fitted a cheap after-market one to our car a year or so ago. Quality is pretty good, and the low-light/night performance surprisingly so. Wiring was dead easy, just joined to the reverse bulb connection so it comes on when reversing. It came with a huge long cable which would probably be long enough for most campers, I had to shorten it quite a bit (not much room behind panels to have it all coiled up). I went with a 5″ screen rather than a rear-view mirror type, as I have it at the back of the car so I can see it when looking over my shoulder without having to switch between looking backwards and forwards.
That may or not be relevant, depending on the type of camper they have and how they reverse, as you need a forward-facing type camera which doesn’t flip the image. Ignore that last bit if it’s going to be a dash- or windscreen-mounted screen.