anyone else try Flex-seal over Plywood coated with fiberglass? Mine is going strong after 4 years. easy to clean and the black color shows the white precipitates if I don't do so well.

I also saw an image of Clyde Butcher's darkroom and he appears to have had acrylic trays fabricated. An aquarium maker could fabricate a long sink with relatively thin and light materials. I would put a wood frame around it for protection.