Never Built an all glass tank that big, but the 90G DIY I did had the bottom panel floating between the vertical pieces. During assembly I put down a ton of dvd/xbox game cases on the floor, then set the bottom pane on top of them. Ran a bead of silicone all along the edges of the pane and then started adding my vertical pieces one by one. Once all panels were in place I did my interior seams w/silicone(obviously you need to work fast, a helper or two is definately best). Once dry the silicone did hold the bottom pane as well as the weight of all the water. Even if you do build w/the bottom panel not floating, you can always add insurance, such as using a sheet of styrofoam to keep the bottom pane from being directly on bare wood, or even adding corner wood trim to the entire bottom.