I finished my river barge (16' NRS Cat used as a family fishing rig) about a month ago. I made my floors and deck out of 3/4" birch ply. I cut my floor into 3 sections, then routed the side edges. After I cut my sections I spar urethaned the bottoms and sides with 5 coats. Then I taped off about 1/2" from the sides and Herculined the tops (I didnt want the Herculiner rubbing against my tubes). I did the same thing for the deck.
They turned out great!
(shitty cell phone picture)