Issues with mana management as a Elemental Shaman in dungeons

I'm currently a level 64 Ele Sham in Cata Classic and have been having pretty big issues when it comes to mana management in dungeons, from what I understand the best rotation when it comes to groups of 3+ mobs in dungeons is to just spam Chain Lightning however this drains my mana pretty quickly even with Rolling Thunder and Elemental Focus, causing me to either sit around doing nothing but cast Lightning Bolt or sit out from fights and drink to get my mana back, not to mention it's especially bad when groups enter boss fights just seconds after dealing with big packs as I don't even have a chance to try and do my rotation as I don't have enough mana for nearly any of it.

Is there something i'm doing wrong or is this a constant issue amongst other Ele Shams? Is there some kinda glpyh that I need drastically that i'm unaware of?