I countersunk mine also and they wers still fine after almost 50 hours of flying. Since the hinges didn't have to close completely I didn't countersink the full depth. The screw heads were out about 1/32" from the surface of the hinge.
The original hinges used pan head screws. They were staggered so that the screw head from each surface was about a half inch off of the one on the other side then the hinge was drilled to allow the head of the screw to go in the hole when the hinge was closed. That worked good also and showed no problems after the original 114 hours on the plane when I bought it.
