I was thinking (if I were trying to design something that could theoretically be used in-game) they would be on the bottom platform, where the boilers are. Two heavies, front and back. Then a light on either balloon, probably facing the sides. The ship would be crazy effective head on, but would have almost no defense against someone above and behind it...
But, I figured I'd just try to make it look as cool as possible instead. Needs some big engines next, then lots of detail.