I belive I'd just stick with two 12s instead of one 24. I know they make a 24v battery but I've never seen one and wouldn't be very easy to find with enough cca to equal two 12v batterys.
Speaking of 24v, I never understood why 24v never took off in the civilian market. Exspecially on the big rigs. 24v is alot better in my opinion. You can run the same equipment with 1/2 the amp draw.