I would recommend searching on ebay or amazon "gopro hero 5 session diving lens" and then cut out a square piece of lexan and insert that into the housing. That's what I did with my gopro hero 5 session and works well to protect the lens, it's the same as brain exploders (don't know why people don't just do this), it's cheaper, the housing is less bulky and its not made out of questionable 3D printed plastic (plus if you ever go diving you can use the lenses it comes with )
Better yet, heres a link: https://www.amazon.co.uk/CamKix-replacement-Diving-compatible-Session/dp/B018DODPVU/ref=sr_1_3?keywords=gopro+hero+5+session+diving+lens&qid=1553452878&s=gateway&sr=8-3