Hi surrealism. I used the egg crates for my false bottom. I cut it to the size of my tank, just a little maybe one square shorter so i could get it in. ziptied them together. made four sides and one on top. how i got it in best was going through the top of my viv, (I dont know how urs is shaped so it may work diffrently) To help keep things going through the holes i covered it in window screening. Personally i put expandable foam on mine for terrain and it created a tight enough seal, I kinda had to shove it in..lol made a very annoying squeky sound but its been good for keeping the sides a little tighter. I personally didn't use legs just made it as tall as i needed instead of legs proping it up. this is how i did it, hope it helps. IF my explainations confusing..im horable at explaianing things..let me know.. hope it helps.