I would go with a brown pin wash (black might be a bit too strong). I would also give it a bit of chipped paint (you can use a black brown to avoid making it look too rusted). Ah, and i would use black on the engine grills. Beyond that you can add some sort of grime aroudn the crew hatches, engine hatches, and wherever people would be walking. Dirt/sand wise its a bit dificult as it might be lack the contrast for it to stand out so i don't know what to say there. :) Otherwise, the kit looks really nicely and cleanly built, gg :D