Welcome to the family, good luck with your new ride.
I have a Cougar FTD with the dual 26 gallon fuel tanks. 4 Group 31 batteries fit no problem. They are mounted in the Bass Cat alum. battery holders right alongside the fuel tanks.
I looked at my buddys puma ftd. It has a bridge built across the sump for the oil tank. Actual looks like a cutting board made from plastic. Also looks like a double aluminum battery tray was added on one side. On a side note. If you drill holes be sure and seal those holes. Appears they mounted the tank holder to the plastic right in the center of the rigging hose.
So basically a mounting plate built over top of the bilge pumps and then bolting the oil tank to it to allow room to mount a 4th battery. Thanks, I will be interested if BCB offers this or if it is a local mechanic fabricated product.
Call BCB. Ask for Richard. He Will assist you in any way he can. He is a great guy and a wealth of knowledge. He does stay busy! Though if he dont answer leave a message and number and he will return the call!