Re: how to install pedastal seat
The center of the pedestal base is about 3" in diameter and hangs about 2" under the deck. Another possibility is to build a storage box, attach to floor, and mount seat on box. Now, if you really want to get creative, make a round seat mount out of fiberglass (use a small trash can as a mold), attach to floor, and mount seat on it.
I mounted my pedestal mounts on my new floor before it went down. Glassed a 10 wooden donut underneath the mount spot, then glassed in stainless capture nuts. The mount is now 1" thick, leak free, and rock solid. Much easier when floor is out, though.
As an aside, I really like the pedestal seats. Makes the interior look bigger. Easy to remove for storage. Can pop the seats out for a flat surface during an over-nighter.
Enjoy.