How do you defeat the Ancient Rock Wraith in the Deep Roads?

I also had issues with this battle using a party with no tank. A few things helped me finally beat it:

• Whenever a party member is targeted for melee by the rock wraith, kite him around, he'll do much less damage if you just stay away from him and let your ranged attackers continue to do damage.
• Watch for him to form up into a shield, as he will then do a fast rolling attack targeting one party member. If you can figure out who he is targeting, its an easy dodge by running perpendicular to his charge.
• Save your aoe/damage over time spells (i.e. Firestorm, Tempest, etc) for when he falls to pieces in a rock pile. He is immobile and will take full damage.
• Focus down his minions that he calls in while he's in the rock pile state first, before attacking him directly. Once they're all dead, focus all your attacks on the rock pile.
• Lastly, always pay attention for when he will do his AOE shining light attack as it causes mass damage that is hard to recover from. Successfully hiding behind a pillar for this attack makes a huge difference.
• Chug potions like there's no tomorrow. If you have any poisons for your rogues to use, drink them too.

This is easily the hardest battle thus far into the game.