Looks like I am going to give the 6v battery world a try. I currently have have 3 optimas w/ 165 amp hours.
I can put 2 6v US Battery - US 125 XC in series to create 12 volt bank with 242 amp hours. That is like having 4.5 blutops for the stereo.
Cost per US battery is $100. So I am paying 82 cents per amp hour. For the savings and additional power...I can manage to check the batt's and refill them. My situation allows me to mount the right side up - the only way you can do it with a wet battery.