I added a rear view camera to my rig a couple of years ago. Originally went with the el cheapo Walmart wireless one, and had same results as Reddog1. Dismal. I suspect most of my trouble with that one was due to the aluminum siding on my camper blocking the signal. It is now sitting in my shop until I figure out what to do with it.
Later added a wired one and love it. It was actually cheaper than the Walmart one but works a thousand times better and has a much bigger and better picture. Anyway, I mounted the monitor on the sun visor. Whether towing or not, I like the ability to be able to glance at the monitor every once in a while like I would a rear-view mirror to make sure everything's ok back there (sometimes I have my motorcycle on a rear rack, or carry my bicycle back there). It also helps with passing vehicles that might be in my blind spot otherwise. I often spot them on the monitor with my peripheral vision. I find it to be a great addition. And obviously, it helps greatly with backing up.
CameraMonitor