If this thing is to work on water I had better sort out some steering. The easiest way to do this appeared to involve a ready to use rudder as found on the racks of most model boat parts suppliers.
It's only when I came to fit the thing I realised that they are designed to be used in boats with nice deep keels and decks and no campers with only a thin bit of plastic between the inside and outside. This left the nylon tubed far too long. In fact even when I shortened it as much as possible, so that there was only just enough threaded section for the retaining nut to grip there was about 10mm of tube above the plastic.
While I could have abandoned this and scratchbuilt a rudder, or acquired a Robbie version which I think is more amenable to this sort of application, I just fitted some plastic tube around the nylon shaft so that the nut could be tightened up fully onto this and grip the interior. Then copious amounts of epoxy glue were smeared around to keep the water out of the van. Leakiness is not something I want to emulate from the prototype !
Standing the model on its wheels required some trimming of the brass paddle with tin snips though.
Purists will note that the real vehicle was controlled using a barge style tiller hinged on the back or an outboard motor when the van engine failed. My rudder may be in the wrong place but one painted black I doubt anyone will notice the subterfuge. And if they do I don't care as making a tiller work is much harder and as I always say, this is my model, if you don't like it, build your own !