I've only seen ONE bench in a shower that wasn't covered in bottles and shower products. It was in a resort hotel. In Thailand. It was a steam shower. The bench was for boning. I know this because we boned on it as soon as the concierge left after showing us how to turn on the steam shower. There was probably a camera in there, because I'm certain that's what everyone does in that shower. But yeah, I agree with the others that a removable teak bench would be your best bet at this point. I know it's shitty to have a plan and completely forget said plan, but aside from ripping out the work you've already done, this is your move.