I believe it is a time-period contract for the most of time, especially with defending crewmembers. You always need a good engineer who knows your ship, but you can cheapskate with wages when it comes to guards and the like.
Mercenary bands probably are trip-hired, but mercenary companies offer longer employment and a place to bunk and eat in-between.
Military ships are most likely unit-based with a term of service.
I think the means of employment on a ship are as varied as there is needs for a crew to man the positions. Crucial members are more rigidly tied to their ship, while less-necessary people might be hopping from ship to ship at a constant basis.
Clothing is probably varied depending on the location people fly in. Tinted goggles and well-tied hats are a must, but the warmth-factor of a clothing depends probably on the region and altitude, which should be told by the captain.
Edit: Also, how in the seven hells did somebody get the idea of mounting a field gun on an airship? I mean, familiarity factors aside (I'm artillery corporal) that is pretty jury-rig solution.
