I am thinking of doing the same project on my Watkins 27. My galley counter top has rot after the PO neglected to fix a leaking stanchion. Mine looks to be simple laminate over ply. My plans are to remove the existing and use it as a pattern for the replacement, however, I want to relocate and recess the stovetop to increase my counter space. I am probably going to go with 5/8"-3/4" marine ply and tile for finish.
I would be very interested to see how your project progresses. So make sure to keep us posted...
1983 Morgan OI 416