I just clamp it and then seal the inside, and after its all dry i go around the outside seams as well. The way i do the base is kinda unique. Lets say the footprint is 48x18. I cut one piece 48x18, and then another 47.5x17.5 and glue it ontop of the first. This leaves me a nice 1/4" lip all the way around the base and makes it super easy to assemble from there. Having the bottom 1/2" thick on all my tanks makes them heavy, but strong. On smaller tanks, i only seal the inside seams, nothing between the glass. I have built close to 300 this way with no issues except one time when i pressed my luck and had a 125 bust that i build out of 1/4". I know.....bad idea.Pharaoh;3700697; said:Great looking tanks. One question... how do you space the seams when building? or do you just clamp and leave?