Thought i might throw my opinion in here
Ammo: Lesmok, Loch, Greased (have your gunner bring a wrench)
Lesmok will allow you to start peppering your foe earlier, and greased will give you and extra shot and let the already fast shooting Hellhound shoot even faster! Less damage yes, but a faster stream of damage. And of corse, Loch is a thing of beauty, just make sure your gunner hops off the gun and gives it a whack during that reload cycle.
Captain tools. Kerosene, Claw, Chute Vent.
I feel the first 2 tools have been explained already so let me explain the 3rd. A Goldfish's balloon can take a good deal of punishment from non balloon-popping weapons, and from your captain tools, so if your close up on a foe that is about to turn to face you with its guns, drop out of sight, and pop back up in his blind spot! If they do shoot at you while your going down your already hardy balloons will take the damage!
This principle also applies when approaching enemies. Im not sure of the top of my head if the the hellhound has a good upward arc, but if you approach enemies from below you can use your balloon as a shield, absorbing damage as you approach, then you pop back up after a pass bellow, and hit them with a loch to get there engineers in a fuss right off the bat.
Edit: After looking a little more at Incediary, i think you could easily swap it out for Lesmok. Heavy is also a great idea, but i still like greased. Personal preference even if a stupid one