Hi Dave,
It can be done, at least with a Mustang.
This is from a pic I took this weekend. It looks like he basically cut the car from the frnt edge of the rear quarter, leaving the door jamb area intact, cutting also the C pillars.
The rear springs will have to be rethought as there will be much less weight over the tires. Maybe a quad shock system can be made so the trailer is not so skittish over the bumps.
You can also see that the dual exhaust is maintained, also the rear lights probably work also.
It looks like some sort of tonneau cover is rigged up but a flat piece of metal welded in will work too but you just have to see how flat that panel will come out.
You might want to PM moparclown or 71RTSEWagon-Conv to get some ideas.
Have fun!