For years I have looked for an closet outside hatch for a Scamp-13. None that I had found took full advantage of the limited space available. I recently found a hatch that you could order through West Marine which fit the space.
The hatch is a Tempress Cam Hatch 13 X 17 O.D. It sell for $82.99 with free shipping to the store. Tempress also sell a lock fot the hatch for about $12.00.
I centered the hatch on the available space but if I were to redo it, I would mount it about .5" aft. There is also a slight bow to the body and I may add a 3/16 shim to the bottom edge of the hatch. I will try to attach pictures of the install and it took about 1.5 hours to center and cut the hole.
TEMPRESS Access Hatches with Slam or Cam Latches at West Marine