Re: Mounting swivel seat base to aluminum bench seat?
I think the aluminum of the seat bulk head would be too thin and make for a wobbly seat mounting platform. Lean back in the seat and the aluminum would flex, eventually pulling the fasteners loose.
I did something that I'm sure you won't want to tackle. But,,, I cut a hole in the seat bulkheads, bent a lip around the opening to add rigidity to the opening (not easy), filled the interior with sheet foam to replace flotation and create a storage compartment. I used 5/8" plywood as a lid and this serves as the seat mount also. That said, I wouldn't go hacking into the seat bulkhead unless you have the tools/skills to bend a lip all the way around the opening or it will be very weak.
This isn't a great pic of the seat and lids, but will give you and idea.
On the front seat bulkhead, I just made a piece of plywood 12x18", T-nuts from the bottom, covered with vinyl, then used 8-10 screws to secure it to the bulkhead. Though, this is just for kids and not use while underway, since it's right at the bow. You could make a mounting plate like this for the other seats, just be sure to make it wide enough so the load is distributed well. I'm guessing, but maybe a 18x18 or 16x16 piece of plywood.
