I have the same problem. I recently purchased a new tow vehicle. It is a 2100 F-150. It does not have the factory back up camera. With the rear seat head rests and the tool box I installed in the back of the truck you can not SEE A THING BACKING UP. Besides backing over some kid I also can not see backing out of a parking spot. I have just been backing up blind and hoping the on coming vehicle stops. I had a installed back up camera on my last truck but, it only lasted until the first Minnesota winter came along then it was junk.
I also do not have the room in my new truck to mount a screen.
From the responses I see on this thread so far it looks like backing over some kid on a bike or into another vehicle are my only options.
I hope more people will respond and I can find a better quality, permanently mounted, back up camera.