The build up is concrete base, dpm,40mm PIR foam, 3mm foam underlay and then 22mm flooring grade chip. Too late to go back and channel the concrete for the shower waste.
Ideas so far... bunch of fully threaded woodscrews with the tips squared off and carefully measured to just reach the concrete. Won't do the dpm much good but...
Undermining the foam and filling with cement slurry. Corner location with only 10 to 15mm edge clearance.
Stiff metal sheet with folded edges to screw to wall studs and flooring.
Any other suggestions/experience?