Re: Opinion on aluminum boat modification
Yep removing the bench seat without adding back some alternate support was a big mistake.
If you want the open floor space to use as a fishing platform, you can keep the center section open, and add two Jump Seat style seats to the side that double as supports.
Cut plywood or aluminum triangle shapped braces, say about 20 inches tall, and 12" on the bottom. Make them conform to the hull sides and floor so they can be through bolted to the bottom rib and up along the gunnel. Put two on each side, then add a horizontal seat base to them. You should be able to sit with your back against the gunnel, and still have open floor for walking/standing in the center. This will add back enough support that the sides will not just collapse in when you get two big guys standing next to each other in the boat.
Kind of hard to tell the size from the photo, but my guess this is about a 12' boat, with 5 foot beam, right?