I used fiberglass for the first time to make speaker brackets. Took me about 4 hours total including drying time, and they worked great. Since they're not in a location where the brackets will be visible, it's a lot easier to work with. I just bolted a t-shirt (you read that right) stretched tight across the location the speaker was going to sit, then spread fiberglass resin on the shirt and let it harden. Once I had that 'mold' hardened, I used a dremel to saw out the location for the speaker, then fiberglassed the whole thing. Lastly was just drilling and screwing the speaker to the new bracket (and some light sanding). Worked perfectly.
