First, keep in mind that Eranikus is immune to nature damage. So your shammy will rely only on Searing Totem/Flame Shocks.

Second, make sure grounding totem is up all the time. It will absorb the sleep but will wipe you paladin aggro (only his). You will have to Righteous Defense right after it.

The thing that really hurts here, is the AoE stun since grounding totem will not absorb that. The only way I've found to survive that was dps him down as fast as you can. Pretty much doable, downed him at lvl 52 on my pala/shammies team using only flame shocks and searing totems (yeah it was a pain)