Use a laptop and a webcam for a backup camera that I had in the house.
My laptop Lenovo Thinkpad T60
Webcam Logiteck Pro9000
2 earth magnets
I mounted 2 earth magnets to a block of wood and use a old inner tube to hold the webcam to the block of wood. I attach the webcam to the back of my truck and run a usb cord to the cab of the truck, where the laptop is Now I can backup to my trailer perfect every time.When done just remove webcam.
I used Yawcam software on the laptop for viewing.
Yawcam software FREE---->
Yawcam - Yet Another Webcam Software