I'd avoid using starting batteries, even big ones.
Generally 2 6v's in series are preferred to parallel 12v's.
In the flooded cell variety Trojan T105's are quite popular (225 amp hour each), or if you want more and have a tall battery compartment the L16HC is 420 amp hour each for about the same footprint. They are taller, and quite heavy.
You could also go AGM, which don't require adding water, resist vibration and freezing better, don't off gas much while charging, and last longer. The down side is that they are much more expensive. Trojan and Optima are popular.
What are you running now for batteries?
Dodge Ram dually laramie 4x4 w/jake, B&W, Brakesmart.
Kit Patio Hauler 394F toyhauler 5th wheel
Camo 680 Rincon, Green 500 Foreman, Blk twincam Roadking