Best set up for Molten Shell?

Any suggestion for a dual totem user that wants to 3 link it? (It's just not worth it for me to give up a 4 link for this, considering I only use it for the extra armor buff)

I current use Increased Duration. I could use faster cast, I suppose, to get it up quicker, but honestly I run with it up pretty much all the time so the cast time isn't really an issue, especially since I tend to hang back and let my totems and minions do all the work.

Gems that increase the damage from Molten Shell don't help a dual totem user at all. Was wondering if there's a skill that will either make the armor bonus higher or perhaps a crowd control gem like blind or flee would be best?

Thoughts?

Oh damn i forgot about Fire penet ( important )


Here is Molten shell in action ( Kole merciless ) :

http://vimeo.com/69857599