My thinking was, that it looked like it was applied a bit heavy. Not beating you up Alex, just commenting. Our vehicles (which admittedly were LAVs, not M1s) never got that rusty. Maybe a tiny bit here and there, but not big areas of it. More likely to get muddy/dusty, with some exhaust stains. If you chip the paint, most times, it just looked like metal underneath, and even if it rusted, it tended to blend into the paint color-wise, probably because such spots were small. High wear areas (grab handles spring to mind), the paint would be gone, but the metal would just look like smooth grey metal because the constant rubbing of hands kept rust from really getting a good start.
I like the build, just describing how some of the wear on armored vehicles looks to give you a mental image
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If you don't have a lot of references already, I'd get some pics of M1s running around Iraq right now to see how they're weathered.