After all the deck parts and hull part are stitched together, I tack-welded between the stitches. I also made a silly blunder. The parts look really "abstract" if you haven't done this before, and haven't seen how the pieces fit together. I tried putting two parts of the deck together "wrong". There are pre-drilled holes in the parts, and I didn't have them matched up properly-they were one hole "off". After tearing my hair out, and posting an embarrassing question on a Help Forum, I finally got the pieces aligned right. The "Ol Learning Curve" kicks in!
Also, I didn't heed the instructions' warning that the tack-welded parts are fragile, and managed to break a seam. Do-Over.