You may want to call a tile setter or kitchen and bath remodeler. Tile setters build concrete (mud pans) and install fiberglass pans. Remodelers often install fiberglass pans. Either trade should kinda specialize in this. Plumbers only care if pipes are leaking not if water is penetrating walls. Also fiberglass pans are supposed to be set in concrete (mud set) so they dont flex and leak. Good luck.
You may want to call a tile setter or kitchen and bath remodeler. Tile setters build concrete (mud pans) and install fiberglass pans. Remodelers often install fiberglass pans. Either trade should kinda specialize in this. Plumbers only care if pipes are leaking not if water is penetrating walls. Also fiberglass pans are supposed to be set in concrete (mud set) so they dont flex and leak. Good luck.