Finished trimming the hatch this weekend.

I used an adjustable inside corner bead,
http://www.trim-tex.com/product_catalog.php?cat_display=showproduct&id=125 to make a splayed angle cover for the frp, after cutting off most of the mud flanges.


Then I added a piece of aluminum flat bar across the bottom to cover and protect the bottom seam.

This is how the aluminum 1"x1" angle I used at the edges is attached. Locktite PL heavy duty and lath screws. After attaching the screws, I would then remove them and grind them down so they didn't extend farther than the plywood, so they wouldn't interfere with the fit.
