The upper corners are not stressed much by the water pressure. The maximum water pressure is at the bottom of the tank, not the top. I wouldn't be at all worried about the corners. The Eurobrace method is most likely the strongest way to deal with the sides bowing out, but I can't see a real need for going to that much work. And, that method requires a lot more silicone joint surface to get very clean, a lot more trouble getting the glass pieces in place without making a mess of the silicone, and at least 4 pieces of glass to get cut to a very close tolerance on length - a real problem. Hardware stores cut glass accurate to about +/- 1/16 inch, which is not nearly good enough. It takes skill and care to cut accurate to +/- 1/64 inch, which is still a bit too big a tolerance for this job. If I were trying this I would try to use a single piece of glass, concentrating on getting it cut accurately, then concentrating on getting it installed with good silicone joints.