Hi Ant,
You are probably right with a table, but second guess would be a holder of some kind? Looking at bdh2crop.jpg those top prongs could be hooks which a container hooks onto and is then secured at the bottom.
There seem to be no end of things people (or companies like Dormobile and Searle) will mount on the sides of vehicles. I've seen sand ladders, skis, jerry cans and tables all mounted along the sides of campers. There's an
example on Terri Ann's site which had brackets so the door top could be removed from the front doors and fastened onto the side further back.
Seems odd that a table would be on the 'wrong' side of the back door though.

It's awkward to walk around when going to the back door, and it's on the road side. Unless your Dormobile was intended for export?
Patrick