Finally trying to get out of the leecher status with something worth contributing, I searched for a similar post but couldn't find anything.
>>THIS WORKS BEST FOR DoT CLASSES (AND HUNTERS)!<<

What you do is start on the little ledge (the black dot furthest to the left of the screenie) and pull Vann and he will run towards you on the red line I marked (the top part of it) and once he is close but not close enough to hit you, you simply jump down to the other black dot and he will start to follow the red line I marked to come down and hit you. Once he is near again, you simply jump back up and he has to run around again, following the red line.
Obviously this is slightly tricky seeing as he has a (long) stun and his thunderclap if it hits you, slows you down, but luckily these things can be trinketed out of, or, if you are a BM hunter (like me currently) you can use Beastial Wrath to be immune for 18secs. If you try and kite while he still has adds you will probably die as they randomly whirlwind and if they are near you they do a crap load of damage, but even by himself - you probably can't solo so hopefully you have some healers / dps backing you up (which you should if you got all the bunkers and people are ready).
As I said before, this is more of a DoTer / Hunter trick as it is hard to stay away from Vann using a bow / gun / thrown on a melee class and even if you can do that, keep aggro with just a single shot every few seconds with the rest of your group beating on him.
This may be common knowledge to some of you but I though I would get it out there for the people that didn't know anyway.
Good luck and have fun, and sorry if some of my post doesn't make sense, I just randomly typed what came into my head first 