You can see why FIMO was used, it lends itself to modelling curvature. I am particularly pleased with the canvas cover. It has a very fine mesh texture like canvas, formed by pressing a close plastic mesh into the soft clay to leave the marks. It also has that flexible feel of cloth as it wraps over the inner framework.
There is room for improvement in the assembly method that will be applied as I set about making a batch of these lorries (5 altogether). I have started with the wheels, shown in progress below alongside the improvised cutters.
Here is a photo of the lorry at Cliddesden on a trial drive shortly after its manufacture at the Tornycroft factory a few miles up the line..