We want to install a Kohler cast iron tub. We will have a 1/2-inch plywood subfloor after taking up the existing vinyl, etc. Installation instructions for the tub sound like 1/2-in plywood will be adequate. But, since the tub (316 lbs w/out water and person!) will rest on its 4 little feet on that subfloor, will 1/2-inch plywood actually be enough to support this weight? I do not want the tub to "sink" or flex and cause a crack in the interface to the tile surround above the tub. If anyone has had experience installing a cast iron tub, would appreciate any advice.