If I were going to fix it I'd head to a boating supply store (West Marine springs to mind), and find myself a kit of West System G Flex.... It is an epoxy, 2 part, that is mostly clear, and has some flexibility when it is cured..Also, I'd find some solid Styrofoam or even spay in some crazy foam (used to insulate stuff) under the shower pan for support after I fixed it...
The GFlex can be used on a verity of stuff..The plastic roto molded kayak for instance, etc... We use it for all sorts of repairs around the house, boat and RV...
Yes, I do work for West Marine, but not for West Systems...
Good luck with it..
73
Semper Fi
Ed