I will definitely keep bracing in mind, I really don't want to create a mess
I agree with you that the sheer size of the thing might make it difficult to find a place for it... It's almost as big (aside from the height) as the cube I work in!
One other member mention thickness, this is my biggest concern at the moment, I have no difficulties with my ability to support the tank so that the siliconed seams do not separate, but the thickness... Well, i can't do a thing about that without buying new pieces. It's tempered, so I know technically it can be thinner than non-tempered glass and withstand more pressure, but I have to do some figuring to determine HOW much.
Crossing the braces is another hurdle for the 4' x 4' tank... But I may be able to use a methodology similar to izabell depending on the thickness of the cross braces. AHH, unless I can find someone with a broken tank, I would have to BUY cross pieces for bracing... Seems like I have a lot of thinking to do.
It is looking like I won't do ANYTHING with this until after we move (our house isn't even sold yet, so there's no ETA). I'd like to take it with me if I spend a lot of time working on it, I just couldn't stand leaving it behind... This is going to drive me crazy until I can get my hands on those panes of glass!
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 class, 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.