A visit to the local DIY shop later and it had a plywood floor. The holes were then drilled for the bolts to join the two bits together - two at the back and three on each 'inside sill' bit at the front which is quite secure and safe as you can lift the whole thing up by the trailer body and it won't come apart.
The pillars were then capped. Next inner wheel arches were made up out of some wood
to reduce the size and weight.
Electrics
Next step was the lighting which is set up the same way as a beetle - using tombstone rear lights and the stock number plate set up that were up in the attic.
The wires were run along the body and attach to the cars via the normal trailer connector.

The front plywood panel was fixed on using self tappers and 4 nuts and bolts.
It works!
After getting the whole thing in primer I had to move house - 200 miles away.
So a day was spent carrying the two bits down the narrow side
passage and welding them together on the road outside. I then gave it a blast around the block on the back of the bug to see if it
(the bug) could cope with the weight and
everything else was good & safe.
It worked great the next day, loaded right up with stuff and the bug (stock 1600 t/p) didn't find it a problem even up Snake Pass.
There was nearly a few accidents on the motorway - not by me but by people staring as they went past. Since then it has also been used to
move house twice/ tip runs etc etc.
Cover / lid
I needed something fairly secure as a cover and only has two days to fit it up (moved house
again!).
I decided to use plywood as it could bend with the lines of the body top and could be fitted in one piece.
It was attached by welding up-ended bolts to the body and cutting out holes in the plywood. This was then bolted on with large washers being used to spread the weight.
Paint
I found a ford colour in spray cans quite similar to the '72 so I painted it in that.
Some chrome trim I had spare was added to finish it off.
Pic below shows it almost finished the wood was later stained darker and a bumper was been added:

Since we got the van it had hardly been used so I sold it to VW Curtains, so you might see it out and about at shows
like at Stanford Hall above
Nearly 10 years later it's re-emerged on Volkszone &
it's still on the road!