Usually helos are not as heavily weathered as armor. A good dusting, some oil and exhaust stains, and some bare silver for worn paint work well. There shouldn't be any rust since they are mostly made of aluminum as well. Some here in Iraq do get quite dusty and grimy though.
Check out this UH-1H model by 11bee at ARC for a good example of weathering.
Or my dusty HH-60G in OIF.
Also check out this post on the same topic.
Good luck.
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