I played with a wireless back up camera & had problems with signal strength & interference. When I bought my trailer I sent Reace a back up camera system from Rear View Safety
. The camera is mounted above the rear window & has been useful as a rear view mirror. I have not found it as useful for pulling into a campground space - the view is too wide for accurate backing. It is great if you have to back up at a gas station, etc since you can check what is behind you. Also good for seeing the idiots that tailgate inside the view of your rear view mirrors & for pulling in when passing.
I purchased a 2 camera system
(although mine came with a 5" monitor and doesn't seem to still be available) & mounted the other on the back of the RAV4. Great for hitching. The kit included a plug/cable system to go between the trailer & tow vehicle. Overall, I/m very happy with the system.