Here is what I got from Amazon, about $80. I attach the camera to my rear ladder then run the wire under the trailer (zip tied) to the front of my 5th wheel to the pin. From there the wire goes to my back door and into the cab. I use the same wire and monitor for my truck camper but just bought a camera for the TC:
ODGear Backup Camera and Monitor Kit For Car ,4.3'' LCD Car Rear View Monitor Night Vision Reverse Backup Camera Waterproof https://www.amazon.com/dp/B01M6UIS25/ref=cm_sw_r_cp_api_ORreAbCXADT5Q
REARMASTER 12V Cigarette Lighter Power Supply Kit for Car rear view camera and Monitor with RCA connection https://www.amazon.com/dp/B01N2T53ZR/ref=cm_sw_r_cp_api_1SreAbDSDBD4W
ATian Waterproof 18 LED Car Rear View Night Vision Reverse Video Backup Parking Camera Black Color https://www.amazon.com/dp/B015J0CGIY/ref=cm_sw_r_cp_api_BTreAb7ZJD0MG
RCA Plug DC 2.1 5.5 MM Power Video AV Extension Cable for CCTV Security Car Tuck Bus Trailer Reverse Parking Reverse Camera 15 Meters 50ft by HitCar https://www.amazon.com/dp/B00DVZYCZA?ref=yo_pop_ma_swf