I'm putting in a new whirlpool tub (jacuzzi) which has some foam blocks on the bottom of the tub and it is referred to as "self-leveling". There don't seem to be any specific instructions regarding whether a mud bed is necessary for this tub. My first impulse is that a mud bed is always necessary, particularly for a fiberglass tub, but would appreciate the input of those more experienced (I'm just a fairly handy homeowner, fixin' up my old wreck). The floor is well supported, .75 plywood with hardibacker on top. Looking forward to y'all's input. Thanks for all your great help during my lurking period.