I'm sorry, truly. I've read where a BRASS wire wheel is a bit more forgiving. And the secret is to continually move the wheel. It may mean going over the same area many times, but that beats not moving the wheel and bringing the
fiberglass fibers out of the resin.
It's also about expectations. Are you going to
paint the raw
fiberglass, or put something over the top? More layers on the interior are more forgiving. Reflectix and rat fur, or ensolite?