Loose Shower Panels

What are they made of?
Got a picture?
If there just plastic I use this under the panel, roll over the panel with a rolling pin to smoosh it out then tape the seam with blue tape untill it cures.
http://www.loctiteproducts.com/p/12...r-Grab-Tub-Surround-Construction-Adhesive.htm

I am new to this chatroom. You referred to "this"? Assuming there is a picture attached? I don't see it. Second, no picture, not positive on the material. I am assuming fiberglass, panels are about 1/4" - 3/8" thick, has the fake marble look. It is a older house that was built in later 70's, early 80's. Thanks and sorry for the newbie type questions.

Opps, forgoot to add it, my bad.

So I would need to remover the existing panels to apply the adhesive to the panels? I was hoping to not have to do that but since the panels seem to be loose towards the bottom I'm not sure that is possible or an adequate fix.

And without being there to see it hard to suggest how to fix it.
I do know if it's not fixed soon you'll be removing them anyway to fix the mold and rot behind them.