Considering removing existing metal frames and buying oversize plexy glass to mount over fiberglass edge. My upper deck is foam core should i bolt through both layers of fiberglass or or just screw into outer layer with a bead of silicon?
Problem is the plexi needs to expand and contract. That's why the bedding rings are used and holes for the fasteners are usually oversized or slotted. If you really want to do this I would go with bolts and not use silicone. Use a commercial window glazing . There is a thread about preferred glazing manufacturers.