I added one and use it with my factory camera system. Mine is from Camera Source. I wish I had gotten one with the long cable, so I could mount it at the top of my camper to see over a trailer. However, mine works fine any other time. Mine does not come on driving down the road. It is helpful every once in a while backing up like getting pretty close to the back of a camping space or parking space..
You do have to remember to unplug it or plug it back in when you take the camper off. If you want to watch vehicles behind you going down the road, I think you’ll need an aftermarket system. Many of those (maybe all) will run all of the time they are on since they don’t know if you are in forward or reverse.