Careful with the saw, Jerry was correct in saying the hatches had aluminum t bar embedded in them. The aluminum is what is expanding from corrosion causing the "hump".
I cut mine out a couple of years ago. The hump in the non-skid skin was cut away and the t bar removed. The cavity was replaced with endgrain balsa soaked in epoxy. The whole hatch was then re covered in fiberglass.
As far as the gutter goes, I was fed up with those little slots in the aft end of the gutter. They were always clogged and they were not the best design. The tube leading from the gutter to the scupper trough would leak as well and I had to replace some wood framing around the hatch. I will try to take some pics this weekend. I glassed up those slots and made new drain tubes in the corner of the gutter.
The aluminum in this shot did not come out of the hatch it was used as a straight edge
Had some other delam issues
primer coats
done
Have a great weekend!
Geo.