All of this backing advice is great, but get yourself a wireless backup camera. I have one from TADI Brothers that gives me a 120 degree view, with no fisheye effect. And it color hi-res with night vision. It just mounts to the license plate frame and has backup lines on the monitor, just like my F250.
The added benefit is that you can leave it on when your rolling down the road to see what's going on behind you. Helps a lot to determine safe lane changes. Yeah, it's a few hundred bucks, but worth every penny.
Also reduces the "pissed of" mood and shattering of the marital bliss that comes with a painful backing experience.