That's the build done and sprayed with a final coat of Tamiya flat clear...
Well...time to make a fairly simple base.
Suddenly struck by inspiration from some Ferrero Rocher cases I've had knocking around for ages. It's just a matter of spraying the inside, not the outside, for a protected finish. I just had a can of RAF ocean grey to hand, obviously any colour will work. Once dry, mask off and apply real soil (I've had some dried out for weeks) mixed with white wood glue, brushed/slopped on with an old, wide brush. Remove masking tape while mixture is wet to get a fairly straight border. Leave to dry (that's the part I find difficult).
The plan is to catch the mixture still workable enough to imprint track marks, mask off again, dry brush several shades from dark mud to off-white and apply grass tufts. Stay tuned, chums.