ORIGINAL: YHR
Yes I started doing this as well. I paint the tank with a finish called hammered steel, then a coat of redbrown primer, followed by German grey. It really makes convincing paint chips when you use a small flat tipped screw driver to distress the paint, and you can see the layers
If you omit the red primer maybe you get a more 'steel' effect, but lose the higher realism in paint chips. But the method is great to reproduce very thin scratches too: I too used a small flat screwdriver, as well as a small saw (those used on the hobbico handles) to make very thin stips.
I find it more realistic, since you reproduce the same wear process found in real world.