With input from Marco I went with a tractor style design and although I settled on the cab section fairly easily it took a moment of inspiration from Marco who basically suggested I tried the cab on the tracks from a separate vehicle, and hey-presto the final design was agreed. We thought that the vehicle had a lot of character and so was deserving of pursuing further. The next step was to then construct a basic outline for the vehicle in Maya and then work over the resulting occlusion render. I have included the render to show how basic the model was. I then took the render into Photoshop and lined over the top adding all the detail.
I will definitely be doing more like this and may even take one of the other designs from the group and work on that. I will however, probably opt for one without tracks as they were a pig to design and render ;p