I want to make one into a settlement. Imagine a town in the clouds that just roams ever so slowly around the wasteland. Bioshock here I come.
I'd try a missile launcher, fatman doesn't tend to have the range
Be hilarious if you took some pot shots at the airship and later joined the faction. "Well we were just flying over the city earlier and some naked dude was shooting at us with a pipe rifle", "Oh wow uh what a idiot, psh" *looks around*.
Why shoot it down? When you can get on board and take it over!