I re-did the seats ina boat about 3 yrs ago with extrior plywwod that I had coated with resin on both sides and edges. Was in great shape when I sold it about 6 monthes ago. Seal the edges well as that is are very important. I did it too save $$ and I knew I was getting rid of boat in about a year. If you love this boat and plan on keeping it a long time, I would try to buy starboard. More $$ for sure, but last forever with no PITA (pain in the a#@). As far as SS T-nuts try McMaster Carr. (mcmaster-carr.com, I think just doa google search). They have Great prices on all types of stainless hardware.

-Mike

I'm with JohnJan on the Marine grade plywood. For the amount of time I was spending building seats, I didn't see the point in saving a few dollars getting exterior grade vs marine. Take a good look at marine plywood, you'll be hard pressed to find gaps. Not to mention the stuff i found was sanded on both sides with no broken corners. I didn't have to spend a bunch of time looking thru a stack to find a good sheet either.

Lot's of good points in this thread.
DS

Wolmanized lumber won't get eaten by bugs or fungus.... but get it wet enough and it will delaminate... besides... that stuff stinks... get regular plywood and coat it with west system epoxy... works better than fiberglass resin... more money though... but seals much better...You can "reduce" the first coat with a little acetone... it will penetrate the lumber better... wait a few days... scuff and coat again... good stuff... then use all stainless staples and t-nuts.

The big advantage of marine grade lumber is it is so damn flat and straight... no bows or warping... for small things like seat bottoms... if you are using 5/8 or 3/4... the regular plywood is way strong... if you are trying to make everything thin and light... definitely go with the marine ply..

Use regular plywoods and coat with fiberglass resins, and do be sure to seal all cut edges. Use stainless t-nuts and staples with pneumatic stapler.

exterior ply is fine if coated. I may try this on my next project.

http://www.elfproducts.com/press.html

Marine plywood is the best if you can't properly seal every little place water could enter. Using a good grade plywood and coating it with cloth and resin will last many years but remember, everywhere you drill to put the tee nuts in will allow moisture in. You can't completely seal moisture out if you drill holes in it. Most boats use exterior grade plywood in stringers and than cloth and resin and after 20 years the plywood is like new. But all screw and bolt holes must be sealed. You can't seal the tee nuts properly. Also keeping the boat covered or inside storage when not being used helps.