To achieve the weathered look, apply Silver paint to the selected areas first to simulate paint wear, and when that touch-dries, apply a little red oxide paint over the top to simulate rust. Another tip is to paint some red oxide underneath a hinge, etc, and smudge it down with your finger to simulate rust that has washed down over a long period of time, like on this HISS tank;

__________________
"The future's uncertain and the end is always near." - The Doors "Roadhouse Blues".