Square pedestal seats

I have a Broom speed boat,the seats were mounted on ply boxes with angle aluminium screwed to the deck.They have stood the test of time,but have eventually become rotted.
I have two new pedestal seats that only have a 8" square base plates.
The deck is a sealed waterproof section between the deck and the hull.(bouyancy?)
I've sealed the screw holes in the deck with epoxy.
I don't want to cut into the deck to reinforce it for the pedestals.
I am thinking of adding a few layers of strand matting to the deck to thicken and strengthen where the seat pedestals fit.I'm thinking of maybe 3 or 4 layers.
Has anyone had any success with this method?
The seats swivel,and when fishing,they are turned to the stern.
I took the back two seats out to make more space.
The drain bung drains the deck,not the sealed cavity below the deck.