Paint the whole thing. Probably an oil based paint would be best for water proofing.
I was making a stitch and glue pirogue and thought this could easily been made at a smaller scale.
Step 1: Stitch sides
Use card board from a legal pad. Cut off the end that held the paper. Cut 2 one inch strips from the long end of what remains. Cut a small portion off each end at about 35* angle. Place the two pieces evenly on top of one another. Place a piece of tape at the ends, securing one piece to the other. Bow the two pieces away from one another. Insert a 1/4"x1" piece of left over card board between the two pieces to hold the sides apart.