I figured out how to get a 10 foot sink out of a 8 foot board.
I had also desired a 10 foot sink, but the cost of a 10 foot piece of plywood was alarming. Since I had decided to create a 32"x10' sink, I got a regular 4x8x3/4, cut two 32" sections off the length (size 32"x48") cut a 24"x32" out of the piece that was left and two 8"x29" from the remains. Putting the 32x48's on the ends, the 24x32 in the middle, with the 8x29 overlapping the joints. Lots of exterior glue and screws. The sink sits on a 2x4 frame. I use 2x6 sides on the sink (I had read somewhere that you should provide a wide board so you could lean on it when you were tired) this works well. Placed coving on the inside joints to give a rounded corner effect. Covered the sink with several coats of epoxy paint (marine epoxy from a boat supplier). I have been using this sink for the last 1 1/2 years, I don't think its possible for it to leak. Its great to be able to place 16x20 trays, (20x24 will fit) without worrying about spilling (considering I'd previously used the kitchen sink and counters).