After painting the main body, I realized that the top and rear part seemed empty, so I kitbashed and added a wrought iron chest on top and a gas tank (or petrol tank as the Brits would say) in the rear.
Then I started weathering the mole. First thing was to put mud on the drill. Later, I added rust and metal highlighting.
I then glued/green stuffed the mole to the base and voila.
Addendum: I added "steam" to come from the front nose using a cotton ball. Please vote for this on Coolminiornot.com, with 1 being the lowest and 10 the highest, here.