I'm replacing a Kohler Memoirs whirlpool (which was defective) with another. Plumber "A" installed the drop-in tub using a mortar base as the "feet" of the whirlpool were about 2.5 inches off the enclosure floor. Plumber "B" removed the old tub and mortar. The second tub was again dropped on the enclosure lip, the "feet" were again off the enclosure floor, and he elected to use an expanding foam between the feet and the floor. The install instructions stated that either a mortar based or wood shims could be used. I'm not sure if Plumber "B" method is ok or not. I'd prefer to not fall through the floor while using the whirlpool, or have the tiled enclosure lip break. I'm thinking of placing wood shims under the whirlpool at both ends and the middle. Maybe this is too much -- I just don't know. All advice would be greatly appreciated.