[Zedn]

I reckon mikes way is the go with foam or some thin ply. You dont really need a gutter as such, just a lip that sits a bit lower. I would use two strips of thin ply as a spacer that sits flush with the cutout and then another piece that sticks out about 15mm the whole way around the opening. Glass over the top and then use the pinch weld bubble that has the bubble at right angles to the pinch weld. you could add a little bead of sealer inside the pinch weld to make sure it seals.