You'd put the hatch on the side, and in the "open" position it might just cover the ports for you and look all stylish!
As for the redstone. What type of "salvo" ?
For arrows you can use a dispenser, just hook the dispenser up with redstone or a block adjacent (not diagonally, usually... ) with a fire button (or lever if you want it to keep firing until you turn it off / run out of arrows). You can have lava poor infront of the dispenser so the arrows will come out on flame (warning, fire may be hazardous to your airship. insulate it with rock/obsidian/non flammable blocks 2 out - they throw cinders).
If you wanted to shoot something else. You could make obsidian cannons that fired tnt blocks out. You just have to set a couple up inside, separated. ignite the back one first (with redstone through the obsidian lining) and then the other one a moment later. They both activate, the first one pushes the second out and it'll blow up somewhere outside. WARNING - may piss off your neighbours as it'll pwn any land nearby.
The second "salvo" block doesn't have to be tnt, but it does have to be "loose" ie, not stuck to anything or it'll just get blown up.