That's cool, John! Are you planning the a similar built- up fiberglass flange for the toilet and vent pipe? I suppose on the toilet flange, a steel toilet plate could be incorporated into the mix.
If anyone is curious, you can check out my wood core fiberglass kayak building journal to see some epoxy / fiberglass construction. Plywood is much easier to work with than the cedar strips I usedin the boat.
Boatbuilding Journal