I went with the hard-wired camera system.
I purchased my set-up from EBay
I bought a 7" Pyle monitor with wiring and license plate camera for under $65. Then, I bought 50' of A/V cable($12) and extra camera for $17(photo below) to mount on the upper rear of my Toy Hauler, over the ramp door.
I used a small section of aluminum angle to make a camera mount; and installed it over the center marker light.
When not towing my TH, I connect the A/V cable to the license plate camera on the rear of the truck. I use this camera to hitch up to any trailer.
I feed 12 volts to the camera activation wire(normally connected to the back-up lights). This way, the camera is always viewable). When I'm towing the TH, I can see what's behind me while on the road. This helps while making lane changes. I also use it to back into the camp site.