Securing to the deck will be with screws. It's possible that one of the screws (usually the most rearward one) could be a through-bolt, but I'm not positive on that. Most, if not all, though, will be screws. Pull out the lower rubber gasket and you'll see them. As far as how each section is attached to each other - not sure. I would look for screws in the inside, upper corner... maybe remove the side gasket... once you start poking around it should start to make sense.