Wireless will be expensive for a good system. I decided on a wired system and bought the following from Amazon. Affordable and you can turn on the monitor whenever you want. Good for when you want to see behind you while on the road, especially when passing a slow vehicle so you can see that you are safely ahead. You just unplug the wires when you land at camp and unhook the RV. I ran the wires from a mounted camera (on my rear ladder) under the trailer and zip tied them to the front of the trailer. Everything is mobile and can be temporary or permanent as you want. Good luck
Camera systema better cameraCig lighter switchWire extension