TThe guy that I bought it from just closed the tailgate on his truck to secure it. I added D-rings to the front sides of the camper, and I close the tailgate... I like an 8ft truck bed.
On mine, the plywood that was cut to make the hatch is covered in plastic and fits back in the hole - supported by flat aluminum on the outside. You can see the part of the plywood cover on the bottom right of the second picture.