I helped my buddy remove the middle bench seat out of his older V bottom boat. The middle bench seat was filled with foam insulation to provide floatation. After removing it, it did make the sides of the boat a little less rigid, but not enough to worry him. We put a flat floor in the middle using treated decking board to run in-between the bottom ribs, and then screwed quarter inch plywood down over them to give the floor a surface to walk on. He then used a vinyl flooring attached with paste on cement to cover the wood. All in all, it worked out pretty well, and he hasn’t had any problems with the boat. One thing you could use if your worried about floataion is some rigid insulation board under the plywood, probably the pink “celotex”. Good luck on whatever you decide to use. I would be more concerned about it if your using it on rough water, but if your just pond fishing, or river fishing, its probably not that big of a deal.
SEDNERB