I am now at the stage of having the bed base in place and the sink unit and
I have now removed the centre back seat.

The intention is to use the space for a porta potti and then remount the
seat in reverse over the top of this.

Seat belts are not an issue, as the vehicle is old enough not to need them
in the back but the question is the security of the reverse facing seat
(inherently safer than facing forward in the other two)

I could make a sturdy wooden frame, and Martyn don't lecture me about fire
hazards there's enough timber and varnish in there already. as the existing
frame won't do.

Or would I be altogether safer in getting an iron one welded up ?

What for instance is the position regarding MOT. This thing BTW is not now
nor ever will be registered as a motorcaravan as all the stuff comes out
with a few screws and wing nuts, in true Land Rover tradition.