I have tried a little airbrush weathering for the first time and I must say I did enjoy it 
I painted on the scorch marks around the RCS thrusters with black and Tamiya Smoke.I also dirtied up the airframe a bit with the same smoke colour.
[ATTACH=full]6718[/ATTACH]
[ATTACH=full]6719[/ATTACH]
[ATTACH=full]6720[/ATTACH]
I'm going for something between this..

And this..

On to clear and decals, then more weathering 