New Shower and Tub Questions
Fiber glass shower pans are usually set into a mortar bed so the thing doesn't flex when you stand in it.
No liner needed under the pan.
Pan is set on the subfloor---the new floor covering goes in after the pan--this hides any gap between the pan and subfloor.
As to your bathtub question-----cast iron will give you the longest life while looking good.
Fiberglass looses its shine within a few years if used regularly.
No special support is needed ---just follow the manufacturers instructions.---Mike---
New members: Adding your location to your profile helps in many ways.--M--