What are the overall length and width required? if you're dead set on fiberglass Google
Fiberglass Sheets and cut out the shape you need. I'd lay a piece of welding rod along the edge, wrap it with fiberglass cloth and resin it to stiffen it up. Wear gloves.
Alternatively, you could use
Polymetal.
The enamel-finished aluminum gives a finish that would require molds and vacuum to produce in fiberglass.