Second (third? sixth?) the hacksaw blade in a sabre saw plan, and of course the tape.
If you can, try to drill your starter hole in such a way that it can be part of your lift handle or latch. And if you can do the cut in one shot. If you have to cut from two ends the cuts won't always line up perfectly, esp if there is come thickness to the material you are cutting. Cut real slow on the corners to avoid bending the blade which will put an angle on the cut.
We've done this with good results, and molded a drip channel that we attached under the cutout to keep rain water from leaking around the new hatch. It was part of a repaint project, and once we applied the new nonskid around and on the hatch cover it looked original.