About 20 years ago, I did mine the same way as Ed described, following directions in "The Darkroom Handbook" (Dennis Curtin & Joe DeMaio). I don't remember if I got the fiberglass resin & cloth directions there, but the book had a good frame layout that I used. I also painted the inside of the sink white using marine paint. I had it for several years before I moved and had to sell it. It was bought by the guy who ran the local camera shop. It still looked great when I sold it.

One really bad thing about the resin though: the brush was dragging and pulling the cloth out of place as I was brushing it on, so I put on a pair of plastic gloves and started working with my hands. I thought it felt really warm and was dismayed to lift my hands and find that the gloves had simply dissolved. I had fiberglass hands for well over a full week, maybe two. Also, the sink sides had a few blister areas from where the cloth had sagged and hardened, but these were merely cosmetic.