I start with a smaller base vehicles, but I'd go light. Two hitch balls instead of receivers. The connecting beam in the trailer, which has a stop so it hangs in mid-air with bungee cords for upward rebound. And a tail skid for ground strikes.
Maybe the back (pointy) half of a McKenzie river boat upside down.
I've got the curved sides for a boat tail; just waiting for inspiration on how to clamp onto the rear tip of the drip rails.
