Well, I've been able to put two good nights of painting in now and this is how it's shaping up.
The base colours were done with a mix of GW foundation paints and Tamiya Acrylics, with shading using inks and aa black wash and highlights drybrushed. Evrything was then toned down a bit with an overall wash of GW Devlan Mud. Next step will be to 'muddy it up' by drybrushing a light brown.
Then, if I have time, I'm going to sort out a short section of dirt track as a base.