The instructions call cutting the curve of the galley hatch the ‘only tricky part’ of cutting it out so maybe this will help make it less so. I know the pictures show someone cutting it with a small circular saw and I have a similar one plus a jigsaw plus another small cordless saw. I held each one at that curve and tried to imagine following the seam well enough to make a neat cut. I couldn’t really imagine doing that since you’re cutting on an outside angle and there’s not good support for the saw. Here’s what I used and it worked well.
I started with a small cut (using a 12 volt Milwaukee cut off tool) to have a kerf for this saw to fit into. You can see that cut at the top of the picture. Then it was just a matter of hand sawing all the way down the curve, which was easy to follow. (Just take your time.) The saw is at a steep angle to the wood and only the top corner is in the cut. Since there should only be a little fiberglass and epoxy holding the panels together, it’s not hard. If the panels ‘pinch’ the saw too much just widen the gap a little where you’ve already cut with a thin spacer.
The kerf from this saw is almost nonexistent but you can see it in the picture until it stops near the bottom. Sanding will increase the gap a little but hopefully having such a small gap will help keep water/dust/dirt out and also look neater.