I had a wireless camera on my truck camper but half the time all I got was snow on the screen. I think it was mostly due to my camper's aluminum siding interfering with the signal. Replaced it with a wired system that is always on (I can turn it off at the monitor if I want). The installation is just slightly more involved than a wireless system but it was worth it in improved performance.
You don't need to spend a lot on these things these days if you don't want to. My system was under $50 and works great. The monitor will accept input from two cameras but I'm only running one. You will need more video cable than comes with this for that long of a run but it still should work fine. I have about 45 feet of cable on mine and the picture is great.
I love having it - if I'm towing or hauling my motorcycle on the back rack I can keep an eye on things, and of course it helps with backing up.
CameraDual Input 7" Color Monitor