Thanks! You are making very good points here as well. The base is supposed to be exactly where the tank will sit and not move. The idea of the rag or cloth under it, after making the outline of the platform is a great Idea. I'll see if I can include it somewhere in the steps. Thanks for the contribution 4mm is too thick and won't really help the cement mold to the floor, IMO. Any decent paint store will have it. In fact, if you find a decent strength, big enough supermarket bag, you could use this as well, providing it will cover the surface in one piece. The film does need to be in 1 solid piece, regardless of what you use. Also, any decent paint store will have 1mm or 2mm film. It is absolutely transparent, I just painted it black on the drawing for representation. In fact, a big trash bag that feels strong and resistant will also work for this!! I'll include the new ideas in the main post =) Now.. let's all think about how to do something that works this nice, but on carpet!