If your balloon is under attack don't use Helium or Chute vent to get out of your enemy's fire arc. The balloon damage and decrease in vertical drag will only kill you faster. Call for help and try to get at least one gun on target. Most Carronade ships will break off an attack once their hull armor is breached.
And if you have a buff hammer, get it on that balloon ASAP. It's like both hydrogen and a chute vent put together, except it doesn't sacrifice any HP. Incredibly useful for fighting carronades.
Tough choice. If you're fighting a Carronade Squid, your balloon doesn't go down all that fast. If your engineers can get your balloon up to about half of it's health, you MIGHT be able to raise above the enemy ship using Hydrogen and quickly position yourself over their balloon to give you some time for repairs and counterfire. That requires your ship to be fast though, probably with Kerosene or Moonshine. If you're fighting a Heavy Carronade, this gets even more difficult, but if you know that the enemy Captain doesn't have Hydrogen and isn't expecting any such maneuver, it might work as well.
I wouldn't straight forget about the use of Hydrogen when fighting carronades, it might just throw your enemy off balance to have your ship raising out of a sudden again. If the enemy crew has a competent gunner and captain though, you won't even get a chance for such maneuvers :/ Also, if you're going to do that, check about having two people with spanners at the balloon, because you might easily pop it again when raising.