It is useful for I have a rear view camera on my Escape 17B from Rear View Safety.  Since my tow vehicle didn't have on, I purchased a 2 camera system.  Put one on the back of the RAV4 & the other on the trailer.  They are wired systems that use a flexible cable as the connection between the trailer & the tow vehicle.  

It is useful to see behind you, for example if you need to back up in a gas station, etc as well as seeing the idiots that tailgate insice your rear view mirrors, however it is too wide to be of much use when backing into a campsite.  Since I travel alone, I still "get out and look" at campgrounds.