Squeaky shower insert

[dannyt]

I have a fiberglass shower insert in my upstairs bathroom. Over the last couple of years, the floor has been squeaking more and more. What can I do to stop the squeaking?

 

[Krow]

If you can slide some sort of support between the fiberglass unit and the subfloor, that would lesson, if not, stop the squeaking. The best material would be a mortar or cement.

I don't want to suggest expanding foam unless the base is secured to the floor with no chance of moving. Expanding foam may create other issues.