Best wireless backup camera for 30' trailer

I used a Swift Hitch Wireless Camera System for quite a few years, it's big advantage being both the camera / transmitter and receiver / monitor are each totally self powered and require no interfacing to the vehicle in any way. It can be used for any purpose you want but I used mine only for hitching up and for that it was invaluable. I only sold it last year as my current truck has a built in rear view camera which also serves well for hitching up but had I wanted to use it for parking on a campsite or monitor traffic behind me I'd have kept the Swift Hitch.