Sean:
Most of the weathering on the fuse would be caused by the sun fading the paint and the rain washing dirt and oil off of the fuse. I weather mine perpendicular to the ground. I spray a dark wash or use graphite powder in the panel and rivet lines then I spray a gray wash on the upper surfaces to give the paint the faded, sun bleached look. Lastly, I simulate oil streaks perpendicular to the thrust line because the prop blast and slip stream would blow the oil in the the direction of the thrust line. Here is a picture of a P-47 I did last summer. I have the pictures as larger files that show the details better but they are too large to post here. I can email tham to you if you like.