I know I'm changing gears a little here but . . You could just get one like this http://www.hitchsolutions.com/....html and adjust it any way you want. I go from the boat to the camper and back again in nothing flat, and each have a tow height difference of about 8 inches. Also, you can adjust the height while attached to the truck, takes out the guesswork when towing something for the first time.

FYI, I got mine cheaper, just the first link I found . .