Thanks for the responses everyone, very useful! I should have been clearer that my doubling of AH's I was refering too was based on switching from my old single battery system to a new setup with either dual 6's or 12's. either setup will double my old setup.
It looks like the only benefit to going with the 6's would be durability.
I will do the suggested search on wfco chargers. That may limit my a ability to make the switch as funds are tight right now and having to swap badgers could significantly add to the cost of this!