Thirty years in the building trades, and at least 10 mil. worth of custom homes in the rear view mirror. All I can say is that any plan that would indicate a need for a service access in a shower is one that needs to be re-designed. IMHO, If presented with such a potential situation, I would gently steer the customer toward a safer, more practical solution. If it appeared on a drawing by an alleged "professional" I would not be very kind as I dealt with the source of that cluster-F. I have installed them on ceilings where a stacked plumbing arrangement, in a multi-story institutional occupancy, required them in shower rooms. JMHO, but they always end up looking like shit in a few years. The metal ones start to rust, and all of them end up with condensation on both sides of the doors, and frequently show signs of mold on the plaster/drywall at the edges. Quality spas have access from the front, via well concealed factory access covers.