The GoPro has different housing options:
Three side solid housing
Housing with side openings "Skeleton Housing" that allows an external mic.
Rear Waterproof Panels
Waterproof panel - flat
Waterproof panel - wide to accommodate extra battery or LCD screen
Touch panel --wide
Skeleton Panels Open in the Back to Allow More Sound than the Waterproof
Skeleton panel - flat
Skeleton panel - wide
Frame Only (no front or back)
Frame only narrow
Frame only wide
Maybe there are more. The result is that the rear panel at times needs to be taken off. Guess what ...
Right. More YouTube Videos
Not unlike Barbie doll clothes for different occasions . . .