Thanks dudes! I really appreciate all the comments.
JackMan - I weathered it in several layers over several sessions. The first thing I did was black base the gull grey. Then I used raw umber, burnt sienna, and mars black oil paints mixed in different combinations and thinned down and to a pretty watery consistency then built up layers by stippling with a stiff natural hair brush and blended out with a soft sponge with a little bit more thinner on it. Then once the oil paint fully cured after a few days I spot painted with acrylics. Be sure to let your oils fully dry before applying the acrylic since they dry at different speeds and can ruin your finish. Then I repeated the process until I had something that looked good to my eye. The key is to be subtle and work slowly. Navy jets don't get dirty in a day so it makes sense to me that the same should happen with a model. It's something that takes practice. Also references are just as an important tool as your paints. They set the guidelines for what you want to accomplish.
It also helps that was I an art major with a focus on painting.