Seriously, I wouldn’t use uncatylized sun-cure for this. You need to use regular catalisit because areas that where the UV doesn’t reach will not cure.
Listen to Mako224,dont use it! Go with the regular or even epoxy & some finely chopped glass cloth or fibreglass powder. The Go pro mount on it’s own is all i use & have Go pro mounts on all my boards,never had any problems even in 10ft scottish winter waves. I do use the floaty back door on the camera though,just in case! Go for it…
As for where to place the plug, place it wherever you want the perspective to be from. Shortboards gotta be up on the nose, but longboards could be front or back. If placing on the nose, make sure you have the thickness there. If placing on the tail of a longboard, DON’T use a leash. If it wraps around the camera and some tension is applied, I can guarantee something will break.
I like to install a leash plug nearby (1-2 inches or so) and thread a small leash on to the camera. This way if the plug blows out, you have a backup plan and don’t lose a $299 camera.
Like the other guys said, use either catalyzed polyester or epoxy. Sand it flush and go surf!
I just installed one on the nose of my beater 10’7" for experimentation/learning how to use the camera… just installed like a leash plug really. I don’t think you need any more strength than that. You’re not ever exerting any force on the plug (unless something goes terribly wrong) at any point…it’s just a holder/anchor. I did create a small gap around the perimeter of the hole just below the glass just for good measure. There are other techniques you could use to go above and beyond…all the way up to a proper FCS plug install.