This was quite a quick paintjob - 3 or 4 hours - but I'm really pleased with how it turned out. I took some snapshots while working on it to show the process:
The undercoat is key - one black, one brown from the sides and one bone from above. This gives the model a natural light from above and gives me a lot of definition for free. One could basically just give it a few different washes, pick out some details and call it a day.
This is after said washes, some drybrushing and highlights on the skin. Also painted the metals brown to give 'em a really rusty feel.
Almost ready. Painted the base with homemade texture paint (mix dark brown acrylic colour, some sand, a dash of PVA glue, add a little water, put i a bottle and give it a shake).
Paint base and final details. Easy peasy!