Print with 100% infill, since the walls are not so thick.
You will need some supports, it was designed to be printed on the Gopros Type-C port side. (Type-C printed first, power button side printed last) Mounting hole is M5. The Gopro sits nicely in this mount, snug, but not too tight, i would say its perfect fit.
I have printed mine with 95A TPU, but you could choose a less flexible material which would result in a tighter fit.