Would I get any utility from
GURPS Vehicles: Steampunk Conveyances in coming up with an encounter where PCs are on the ground when a zeppelin from the Antarctic Space Nazis flies overhead?
The zeppelin should have been designed to fit through a gate that cannot simply be scaled up to infinite size without extravagant cost, so it's not monstrously huge, but it should be big enough to operate on its own for a long scouting mission. Of course, nuclear power would make that much more feasible.