Good question which I am now trying to resolve. When I dry fitted it up, it took a bit of stretching around to make the joint line up. I've got some really good contact cement but it sets up pretty quickly. By the way, I would assume the joint is at the bottom center so as to not provide a path for leaks (my nemesis, oil and water).
Right now, I'm thinking to brush the glue on to the metal flange around the perimeter. Then glue and join the ends, fit onto the flange bottom center and clamp so they do not move. Then (from here I'm still figuring out) fit the center top and work my way around each way till it's done.
If someone has a better idea, please chimein