Barry- I have a 6' fiberglass sink in my home darkroom. It is mounted on a square-section tube frame (from the manufacturer) where the tubes are about 1" or so on a side. This by itself is no problem when handling a few trays. However, when I had the 16x20 print washer and the 16x20 Nova slot processor in the sink, the sink started to slump toward the center drain. To compensate, I made a brace that spans the length of the sink. The brace is a pair of two-by-fours running the length of the sink, with a leg at the 1/3 and 2/3 positions, bolted between the lengths. If you want to come by sometime and see the brace, I'd be glad to show you.