I'm almost ready to start shaping the foam blocks into a nice, streamlined shape with the surform and sanding block. To make it more durable and easier to install, I glued 1/4" plywood board with carriage bolts sunk in to the bottom board:
Now I can install or remove it with access to only one side.
I've been building up the shape with more foam board:
I've glued a little more on the sides tonight, and hopefully this weekend I'll get the top board on. Fiberglass arrives tomorrow; once I get it shaped, I'll glass the whole outside, then cut the hatch lid, then do the inside.