I'm gonna break it up with metal panels (some are masked off under the paint) and weathering, but its always just a little scary to commit to such a bold color. I've been expirimenting with different painting and weathering techniques, heres a quick tutorial of one of them:
I first paint over a black undercoat with fiery orange, scorched brown, and vermin brown. (vallejo colors). I use a combination of a large brush an a foam brush. You could also use blister package foam, or offcuts from any of the foam from army storage cases . Dab all over, use lots photos of rust for reference.
Using the foam brush again, I dabbed on liquid latex everywhere I thought damage and paint chipping was most likely to occur. Since this is one of the feet, I figured it would get the most damage on the bottom and the leading edges as the Stompa smashed his way along.
After it dried I sprayed scarfulous (?) brown all over. You can use a regular brush if don't own an airbrush. I actually did on his other foot. Just thin it so you don't remove the latex. Yet.
This time I'm using orange yellow and spraying it on as a first layer of highlights. Centers of flat panels, top edges on the outer foot, ect. Don't go to the edge or spray over areas that should be in shadow. Again brushes are welcome.
This step I highlighted more, this time with bad moon yellow. Don't cover all of the orange yellow, this is the final highlight so use it on the edges, the very center of flat panels, ect. Yes, you can brush again.
Ok, now the fun part! Using your finger, a rubber eraser, a toothpick and tweezers, gently rub the liquid latex off. The paint will flake and chip, thats what you want. The end result will expose the first layer (the rust). Use the toothpick and tweezers to pick off all the little bits of latex and paint chips. Get all the spots of latex, you didn't forget where you put them, did you?