I've now finished off this little project today by finishing off a small base for the models. Nothing fancy but I think it works well in showing off both models and crew. The gun & 1 tonne received a very light dusting of tamiya buff thinned heavily to add a small amount of dust to each. The base was just fine static grass over some plaster & fine sand followed by grass clumps then sprayed with a suitable green and again tamiya buff for the earth.
The figures had their boots dusted with pigments then everything was added to the base. I really like the way this turned out and really enjoyed myself making it.