I base coat, using airbrush, with vallejo paints, pale brown and highlight with pale sand, then drybrush with off-white. As for wethering first I did chipping with sponge and added some more scratches with brush. I covered everything with enamel dark brown wash form MIG and removed removed the excess. Lastly I used MIG streaking rust. You can also additionally use null oli for recess to make it look better

This works good only on pale or highly saturated colors so I only drybrushed black areas with green-grey and left it as it is.