I have a Camos 709 with a 6 input switch so I can look down both sides (4 cameras- 2 in front of 5'er, 2 mounted about 3/4 way to rear of 5'er) one on back of truck, one on back of 5'er. If you look on this page you will see the unit I have - Commercial Backup Systems from MITO Corporation Excellence in Electronics for Auto, Car, Truck, SUV, RV and Boats
You will need transmitters also. I don't remember which ones I used but they were also Camos. You can view the rear of the camper and the sides at the same time. I usually switch so I have both cameras on the side I'm turning to on and one of the opposite side cameras on the display, usually the back one.
I ran my cable inside of grey PVC pipe bought at the local hardware store. Glued a connection wire end on that has a gasket and domed head that make the PVC sort of water proof. Ask at the hardware store they should know what you want. Then used pipe clamps to affix it to bottom of RV. This way the cable isn't hanging anywhere.
The rear camera is up high, cable comes down the back corner to the bottom of RV, covered with Eternabond. Side cameras mounted just a couple of inches above the bottom and cable goes directly into the PVC. Sorry no pictures but I think you get the idea.