So, first of all, I used some cheap acrylic colours to get the redish-brown paint I wanted as a base coat.
Then, I mixed some yellow and burnt sienna oil paint to make the streaks that imitate the wood grain flow. WingnutsWings explains this method on their site and so does Rato Marczak on his:
Finally, I gave it a wash with burnt umber oil paint that is now drying, after which I'll overcoat everything with a semi-gloss varnish. Note that I brush the frame heavily with a stiff brush to give it an worn-out look.
The tank and it's base still needs a few touch-ups too.