Lanefan
Victoria Rules
Or each time there's a reason to be using the gun you just assume they're taking it in shifts and roll to see who happens to be on the gun at that moment. Ditto with piloting - the same person isn't going to be at the helm 24 hours a day thus having two or even three pilots on board* might be a useful thing.Well, the first is an example of what I was talking about, and of course the pilot and gunner are both useful; I was using it as an example of second gunner not being useful on a ship with one gun.

* - which is how we do it in our D&D game where our adventuring company has its own zeppelin-like airship: not everyone in the company knows how to fly it so when we're on a journey in it specific people take shifts as pilot, and if-when piloting suddenly becomes relevant (e.g. we're subjected to aerial attack) we just roll to see who's at the helm right now.