I want to install a tub on basement bath where drain pipes are already installed and sticking out from concrete floor. I need to know how to raise the level of the tub from the floor in order to have enough space underneath to connect to drain without having to break into concrete. The space from the tub drain opening to the floor is 1/2 inch. Are cement board or plywood options to install tub on top of? If so, how do i secure these to concrete floor?