I've got an old 1984 BassTracker Guide Special V-17. The plywood was rotting - so I tore out the entire decking front to back down to the ribs and replaced with aluminum. The only wood in the boat now is the transom (original) and the bow where my trolling motor is mounted (for support). For that I used marine grade plywood, painted it, and then epoxy coated prior to covering with carpet. It's been 16 years and no rotting yet. I redesigned the layout and extended front and back decks adding more storage and a baitwell to boot.
It's not all that hard - worst part for me was cutting the aluminum for the radius on the bow. I used marine carpet and glue...you can get these from any of the big outdoor catalogs I reckon.
My project involved a lot as I added a heck more electronics, aerator pumps, etc. and it did drop the overall weight of my rig by a little over 100 lbs by removing all that wood. Utilize stainless steel hardware to fasten everything.
You can definitely use "retired" road signs - I had a buddy who did just that.