I think I can clarify this for you, it is impossible to place any props down in Zeus, they simply aren't listed anymore, neither are the pre-made bases that one used to be able to whip down from the groups tab. One used to be able to place almost every single item that was listed in the editor, be it a wall, building or bar-gate in order to build missions in zeus, this was a critical and extremely important feature. Now this ability is no more. Since the 1.64 update or there about, this has been impossible.