The plans didn't specify this bend but it looked like a good idea to me.

I wanted both the top and bottom of the hatch sides to have aluminum surfaces. I decided to simply bend a 90 degree angle on each side of the hatch skin. This eliminates the need for additional angle and insures a smooth fit for the weather strip.

To insure a straight bend I sandwiched the aluminum between two 5' long 2x4's and used a rubber mallet to form the aluminum.
Preparing the Hatch Skin