There are several trailer camera options out there and many campers come with standard wiring for the furrion camera system.  There are other options out there… some that are cheaper and some that are better.

Haloview offers a pretty nice system and can use your existing pre-wiring.

They offer rear and side cameras.  720 or 1080 p, crisp color display, front dashcam recorded and more.  You can display the rearview while driving with distance markers for 20,40,60 ft to help change lanes and pass.