When building this pontoon boat, I did a few things I learned in my metal fabrication career. Flex is one of your no no in metal. Aluminum flexes badly. Great for pontoons logs and other pretty things but for a ridge structure , no. A new Bennington came by the other day while I was on my deck in the marina , beautiful . If that pontoon had the design from the floor down on my boat it would be perfect.
The cross members are steel channel.
The floor is light gauge structural metal studs tac welded at each intersection. Running with the flow of the water. No under skin required.
Two 5 foot cone section on the end of 23" od pontoon for extreme lift.
4' Extended 25" tri toon to cut water and smooth water in front two side toons.
Every little weight difference from aluminum structure .
IMO , performance is greatly superior to equal size and equip pontoon boats.