tub enclosure grab bar installation help

I may be called upon to install some grab bars for an elderly person. The tub enclosure stands away from the wall so Ill have to use a grab bar with a spaced anchor. It looks pretty cut and dried in theory. Find the stud above the enclosure and mark down, drill hole. I’m a little hesitant to drill into fiberglass with the wrong bit. Should I use a spade bit or a hole saw cutter or ______________ ?

Anything I’m not thinking about ahead of time? I don’t want to cut a $600 hole.

I would use a Forstner bit that will fit any standard drill. A 1/4" bit will cut a clean accurate opening through fiberglass.