Simon,
If worse comes to worse, maybe you can do what I did when I discovered that my latch recesses were delaminating. (The mat had not been well soaked in resing, I think.) I basically made a male mold out of wood, covered it in resin and then applied mold release. I prepp'ed the inside of the panel: take it down to bare fiberglass, leave it rough and wash with acetone. The mold was held in place by the friction on the sides and you can see the cleats which gauged the depth. The dowels left preformed mounting holes for my latches and held pressure against polished stainless plates, that you can't see, which formed the back wall of the recess. The stainless was predrilled so the dowels also prevented resin from leaking through the holes onto the polished face of the plates. I also left some small tabs on the edges of the SS to provide mechanical grip as well.
Lynn