:hmmm
Bob,
just be careful to be logical with your weathering of the winter cam - the patches you created in your first pass were very strange and not in places or patterns that were realistic.
Now you have a thinner coat trying using some white oils or pigments in a semi dry application [on a wide brush], randomly working over what you have at present, then using a dark grey pigment then very lightly soot black, you can achieve the exhaust and gun stains, but you must be subtle and weather in the direction of the airflow.
?
Maybe too hard to explain - good luck, winter can is always very hard as it either work s or is a disaster - there is no in between because of the extreme tones of white/ dark.
Ian.