Coaming for cabin top hatch dry fit in place. Since this picture it has been epoxied in place. There will be a lip of 3/4" wide x 1/4 in ply added to the top of the coaming fitted flush to the inside of the opening. This will aid in deflecting any water from the opening. The hatch cover will fit over all and contain weather stripping that will (should) fit tightly onto the ply lip. Hinged aft and secured forward with a clamp.
Checking the look of a cast bronze vent for the motor well cover. The vent plus three 2 inch holes drilled in the back of the cover should provide adequate ventilation plus oxygen for the motor, especially at idle.