The egg crate product you are talking about is Delta-FL, it is designed for use in sub floors particularly on cement floors, it goes down first the idea of the egg crate dimpling is to provide an airspace to allow any moisture that will collect under the sheet to dry out. If you put a plastic sheet down on the concrete you will have nothing but moisture problems, mold and mildew, as the plastic does not allow the concrete to breath and thus there is no where for the moisture to go. The sheet is not really designed to have the carpet underlay go on top of it. The load rating is not sufficient for this and you will collapse the dimples. It is supposed to be covered with floor sheeting first you can then put your underlay and carpet on top. You will now have a nice warm and dry floor with no mildew or mold problems.
