If you try DogFish's idea for a 48" x 48" x 24" tank, it will be as strong and safe as a standard 55 gallon tank. The weakest glass is the longest glass, and you will be using those from a proven safe design tank, so they are strong enough. The bottom, I agree again with DogFish, that putting reinforcing pieces of glass across the seams, on the inside, will work fine, even if you don't use a fully supported bottom, but just an edge supported bottom. You will want to silicone seal the whole overlap area, so that will be a very strong joint. And, of course, you will want to Eurobrace the sides to take the place of the standard 55 gallon cross brace.
The only problem I see are having to make a stand that will be adequate and look good, and having to move such a large, awkwardly shaped tank. Good luck, and I hope you try this and report on it.
Last edited by Hoppy; 11-19-2012 at 02:25 AM.