It is a bit of a project to put in the flop tube, with its little trapdoor, relocation of sender, etc, so I probably would only run one. Even if the chance of wanting inverted capabilities later is slim, you should go ahead and do it now. Folks will tell you that you can always install it after the plane is built, but this would involve more than just retrofitting the tank. You'd also have to fab and route new fuel lines, as the location of the tank outlet is quite different.