I really need to get a new digital camera! Anyway, I've been thinking about it for months, and I finally did it. The nice thing is I had all the material lying around the house. Even if you had to go buy the material, it should cost less than $30. I used Unistrut and Unistrut 90 degree brackets as seen here.
I basically just made a wide H shape. I had to trim the verticle pieces at the ends so they would slide into the stake holes in the corners. I used a piece of pipe insulation to pad the upper bar. I just made one for now, for the back of the bed. I'll just put a foam block on the roof for the front. If it works well, I'll make another for the front later when I can, uh, borrow some more material from work. I'll have to try to borrow a friends digicam soon and take some photos.