Here's what I did for a life jacket mount:
I took the base plate that the GoPro comes with in the display case, rounded the edges with a dremel just in case something got loose and flew at me.
Next, I made two 1 1/2"ish slits into the base plate about an inch into the plastic on both sides, which allows the life jacket strap to thread through it as seen in the first picture.
After some unstitching on the middle strap of my life jacket, I was able to move the mount to the direct front of the life jacket. Because I have zero knowledge in sewing or stitching, I decided to just tie both ends of the straps to prevent the life jacket clips from coming off.
Then I added 2 strips of electrical tape to the base plate area where the GoPro slides in to prevent that annoying clicking noise that always seems to occur.
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