The problem is coming up with a leakproof method of going over the dimensions of a standard 8x4 sheet of plywood. My biggest ply-tank was a 900gal (8'x4'x45"). I'm going to try a 120" x 36" x 20" tank by building, basically, 2 separate 5ft tanks with a frame cut in the side of each tank as if I were going to install a glass viewing window in them. But, with a good amount of resin and fiberglass cloth, I'm hoping for a good seal to make 2 tanks into one 10ft x 3ft tank with a 2" ridge around the center of the tank.