I built one of these to pull behind my '71 - I did it in Alaska in 1982.  The
donor car was a '69 camper that had extensive front end damage.  I removed the
camping stuff and installed some of it and the pop top in my kombi.

I cut the body at the rear of the sliding door, but left the frame rails about
2 feet longer.  Welded a steel tube to the cross member just ahead of the
transmission mount and notched, bent, and welded the frame rails to the tube.
Welded on a hitch.

I never finished the opening the way I would have liked.  Filled it with 3/4"
plywood and sealed it so's I could get some stuff down from AK.

Eventually sold it in San Diego for a few hundred bucks.

Keep thinking about making a Vanagon-based one.

-Blaine