The panel was then used as a template against the 4'X8' sheet of fiberglass shower wall. I traced around the top and side with a pencil, then with some cardboard box as a backing (I had it left from the water heater I had replaced a couple of weekends earlier) I used the square and razor knife to score the line I had marked. The fiberglass can then be flexed and will break along the scored line.
One thing I did notice were small vent holes under the upper trays and below the bottom shelf. I suspect they're there to limit condensation inside the door, so I added some 1/16" holes in the fiberglass about 6" from the top and bottom.
I'd like to say it was a breeze to get the panel and gasket back in, but it was tricky. On this particular refrigerator the metal strips holding the gasket slipped out, so I had to figure which way they went back in, the gasket was flopping around, and I felt like the guy on the wrong end of the "flat hose" commercial. I finally figured out to brace the panel about midway up the sides with half-tightened screws, then work the metal strip back into the gasket and start from the top, get the temporary side screws out and get the side metal strips in and eventually work my way to the bottom.