I have a Furrion on my 5er. The camper came "pre-wired" which means, they just tapped into one of the wires for the running lights. When I installed it, I could see the wires.
Lots of folks tap into one of the rear overhead clearance lights, or one of the tail lights.
Doing so, requires you to run with your headlights on so the camera on the trailer will be on. When you turn the head lights off, or unplug from the tow vehicle, the camera goes out.
You'll need to find the wire for your running lights and tap into that. It sounds easy, but may prove to be a harder chore than imagined.
You could potentially run a dedicated hot wire from the battery all the way to the back with an independent switch for off-and-on too. You'll just have to figure out the logistics of your specific camper.
Good luck!