Filling in the back of the Bantam cabin shouldn't have been much more than a scribed rectangle of 2mm thick plastic. Then I looked at the photos and realised below the doors is a towing eye.
I suppose this makes sense, there's nothing else around to use when pulling a barge so I'm glad I took the photo. Oddly, there doesn't seem to be a gap under the raised rear deck for the rope to pass through, but then my photos of this are sketchy 'cos I forgot to hang off the back with the camera. Mind you, the freeboard is so low that if you tie to a barge front, the rope will go up, not down.
Of course, you'll be working with the doors open so it doesn't bear thinking about what happens if the rope snaps...
Anyway, a bit more plastic noodling and a bit of filler to blend the sides together and it's looking fine. Brass wire handles are a guess as I can't remember what should be there but I do recall there was a bar placed across the back to secure the cabin so with my hooks, the arrangement will work well.
