I cut down a spare heavy weapon from em-4 miniatures and then built a little handle rig for it. I then added a shield from Scotia Grendel (it's from the old Void second edition boxed set) as a shield for the gunner. The paint job is very simple -- basic black and a load of weathering. I painted the skull-and-swords logo on the hood; it's a little off-centre, but whatever. The design is inspired by the flag of golden age pirate Calico Jack Rackham. The hourglass symbol in the shield is another pirate flag/gravestone motif.
As you can see, a gunner fits neatly on the step, although it might be hard to fit another model in there. I don't know if this miniature is widely available, but technicals are super-easy conversions.