What comes to P2, shammy/druid/priest combo is just perfect healer composition for the fight. Have your priest spec and glyph into Holy Nova and keep the ranged group alive on the move, this is quite crucial. Druid can HoT the raid (HoTs rule on P2) and shammy can chain heal the melee and so on. What's really important is, that melee NEVER turns their back on the ranged groups - this minimizes the gun damage greatly as melee and ranged should never take damage from the same focus burst. Also, possibly even split your ranged group in two and have them positioned as far apart as it requires for the both groups not to take the same burst at the same time to further minimize the burst damage. After barrages or frost bomb evacuations, get in positions again quickly.
When learning P2, you can also pop BL and try to get through the face as quickly as possible. Although, this requires pretty fast and flawless P3 execution as the enrage timer is kinda tight.