after you figure out what style you want, call https://www.tadibrothers.com/
one of the best companies I have dealt with on the internet. I ended up buying a monitor that was to big, they exchanged it with no problems. I have one on top of back wall of truck camper and one on top of back of box trailer. I went with wireless with external antennas. I power them off the clearance markers. turn on tail lights and cameras come on.
If ever needed, I could bring the monitor into the camper, (turn on the truck lights by press lock button on remote and lights come on for X seconds, or wire switch into camper cord to turn on tail lights) and I can view rear camera from inside camper.