Just had a thought about the fire extinguisher...
If you are a gunner, and you know you are going to face a flamethrower a lot, bring a fire extinguisher. Even if you bring heatsink.
A good flamethrower will focus their flames onto a gun, such that the gun is quickly disabled. And a flamethrower needs only a short window to put 10+ stacks of fire on a component.
And we've all been there. When your gun is too hot to shot. You can call down an engineer, and watch him try to cool your gun with Chem Spray. That's like that guy you called about your internet, not fast enough. Instead, you can let the gun break, and rebuild it, which also isn't fast enough.
Instead, you can bring an extinguisher, and put out your own fires. Unlike engineers, you can do your stuff while extinguisher is on cool down. If the gun gets too hot again, just spray it again, and get back on.
You could bring chem spray and heatsink to try an expert maintenance and keep your gun off fire, but that kinda reduces your dps, and some guns just won't work like that.
So yeah, gunner with extinguisher. A thought.