TBammer wrote:
I think the twin group 24s is the answer.
My tray is exactly like yours, 2 rails on the A-frame, and angled front wall encroaching this space. Three 12V batteries will fit there with one or two inches to spare. Though 3 separate battery boxes might not fit, and it's nearly impossible to find one long box for 3 batts that would fit into those rails either.
Roy is right, you can bolt an oversized box onto the A-frame and place 3 or 4 batteries lengthwise. But, if 2 batts is enough for you, then get 2.