I made one in 1996 for my XR400. I used channel iron for the tray. It was way overkill but I didn't have a way to form metal. I used 1/8" flat bar as an angled hoop for the front tire. There were two problems I had to overcome
1) Getting enough angle to strap it down. With the bike hugging the rear of my Jeep Cherokee and not wanting another bar sticking way out the back, straps didn't work too well. My solution was a slide-in (the hitch tube under the channel) vertical post that clamped to the frame. Roll bike up, slide bar in, tighten bolt. It was slick because even if the clamp had come loose, the bar would have held it from falling off the rear. It might have broken the rear glass but it wouldn't have fallen off. The downside was that it was specific to that bike.
2) The play in the hitch allowed it to rock. A little wiggle translates to a lot at the end of the tray. In hindsight, some shims/wedges in the tube might have worked fine but since I already had the channel iron, I welded tubes that extended under the hitch cross member as far apart as I could. It worked great but added weight.
Sorry, no pictures. It, and the motorcycle, are long gone.
