Perhaps its my gear but this was ridiculously easy with 3 pieces of Frost Resist on each char and the Frost Aura from pally.

Sometimes the debuff would fall off just due to a char resisting during a 3 sec period.

I only have to run behind boulders typically once a fight.

If you are struggling on the boss and don't have Frost Resist gear, I highly recommend you try it with gear.