is what I have.
I have one camera on the tailgate of the truck and bought an extra camera for the rear of the trailer.
I fabricated a holder for the truck out of flat steel stock, spray painted it with black rustoleum, and mounted it over the edge of the tailgate with stainless screws.
I purposely mounted it high for 2 reasons. When using it as a rearview monitor at night, the headlights don't "blind" the camera, and when using it to hitch-up, I get a good angle view.
I replaced the screws with thumbscrews so I can adjust the view so it can be used to hitch-up.
When towing, I disconnect the camera on the tailgate and connect to the cable on the trailer.
I made a mount for the trailer camera out of galvenized steel and then painted it with silver rustoleum. It matches the trailer skin pretty well. I attached the mount to the bottom 2 holes of the license plate bracket.
It's worked pretty well so far.
Another nice thing about the camera on the trailer is being able to see what's behind you when backing in to a site.
One drawback so far - opening the tailgate when the trailer is attached. Camera hits jack head if not careful.