Ok. Progress update.
Taped up the green drywall with green tape.
Pink mud (still wet)
Filled, dried and sanded
3/4" plywood top glued and screwed
Painted with water-protectant
1" foam top
Might go back for a second coat and touch ups. Still need to silicone the base and edges.
The tank is delayed (freight) so might be in next week.