Some good stuff and some bad stuff here, in the simplest terms:

You have some great AE enmity and off GCD enmity. Try to manipulate the first set of adds so that you can utilize both. For the sake of example, I'll tell you what I do.

First, don't hit the head - imo its a waste of time. Slide to the tail, and as soon as you see a splash off the side of the boat, hit Flash. Despite the fact that you cannot target it JUST yet, it will apply 495 enmity to the tail. I will follow that up with 2 un-combo'ed RoHs, which the best enmity you can get in 2 moves.

This should bring you to the adds spawning, if they are nearby: Flash > CoS > Flash > SW (add) > Flash > regular 2-target enmity. If they are on the other side, a great trick is to use provoke while you are running into range of the add, it does not apply much enmity, but it WILL get the add headed towards you, instead of headed towards a healer, giving your DPS more time to hit it while stationary, and you an easier time starting AE enmity on both the tail on the add once it gets back. So, Provoke > Shield Lob > Shield Lob > CoS (as it is back at the tail) > Flash > SW (add) > Flash > regular 2-target enmity.