I did it on my 20g long Pencilfish biotope in last year's AGA. You can see the tank in the showcase. I wouldn't go any longer than 30" without some sort of bracing, even if it's just a 1/2" glass strip across the middle. Be careful with the inner edge of the glass after removing the rim. They don't sand them down and they're VERY sharp. I ended up with many many small cuts after doing my tank.