besides the supports around the tub, you probably want to set the tub into a base of mortar or a sand mix concrete. Don't concrete the drain though. Lay down some plastic. Mix the mortar and dump on the plastic(just a layer a couple three inches thick or so) so the tub sets into it and pushes the excess out. Lay another piece of plastic on the mortar before setting the tub. (the plastic helps with removal some day in the future.