If you're planning on tanking, I highly recommend you bring a hunter and a lot of mana potions. Your threat will be terrible because you'll be out of mana very quickly.
A rogue isn't a bad choice either if they can successfully time a Vanish, but the hunter is ideal for Phase 2 and frequent feigns.
Fight can be pretty easily 3-manned (healer, tank, hunter), and more just make it go a lot faster. (Yes I know the fight can be two-manned or even solo'd, but Petrus can't do that as a paladin).