I'm looking at getting two water storage tanks for my RO/DI water and my mixed SW. I took a tip from Rocketmandb's build thread and found this stackable 70g tank from NTOtank.com. My storage tanks are going to have to fit into a standard bedroom closet so stackable is rather important. That I can just put these on a sheet of marine plywood and not have to build a heavyweight shelving unit is pretty bonus. I plan to make the lower tank the RO/DI so that I have easier access to the tank top lid for adding salt to the salt mix. I plan to use gravity feed to the sump from the salt water storage. The RO/DI will have be attached to an osmolator (or similar) with a pump for ATO and the same pump will be used to fill the SW storage from the RO/DI storage. Any other alternative or perhaps cheaper sources? Is stackable a reasonable approach?