Pressure is only affected by height. Force is increased if length is increased in a panel. You could make a tank with the footprint of a football field that is only 21 inches high using glass from a bunch of 55s as lon as the top is braced effectively. Your idea will work, but I would personally build a plywood tank and use the glass from your tank as veiwing windows. Check out my thread "55+29+55=139 and 10.5' long". You can see the concept at work in that tank.