Can anybody suggest a good way to achieve a similar weathering effect as depicted on the side skirts of this M1?

Depending on which color you have (the lighter or darker shade), I would recommend you mix a little white or tan in with it. A few simple shoots through a fine airbrush should do it.

Thanks Matt

I had considered that

If I am correct, and I hope I am, it looks like this m1 is wet. You might be able to produce it with rain effects then add the dust with pigments or chalks. I would try out Matt's method and then this on some scrap and see what works best. Afv Modeller did an article two or three years ago on the Stryker and it had a wet rain soaked finish. All you should need to do is the same process and add dust. Cheers,
HTH

Just as matt said. Then I'd add a light overall wash and thirdly some slightly darker pin-washes to the panel lines. After it's all dried airbrush a couple of flat clear coats.

Whatever way you choose to do, dont make too much contrast ebtween the differetn shades. It´ll look wrong on a scale model. You can spray a thinned filter over the skirts should this be the case to tone it down.

Cheers fellas. I've utilised some of your suggestions and have achieved a subtle effect, which I am happy enough with. Will post pics in the 'Constructive Feedback' forum soon.

Regards
Greg