The epoxy will not stick to starboard. It is almost impossible to get anything to stick to that stuff including 5200. Try it if you don't believe me.
What you want to do is drill out the holes big enough so there is no possible water intrusion when the screw hole is drilled into the epoxy. I would start with a 3/8' bit or so, countersink as Alloy suggested and then fill with a epoxy, cabosil mixture. Make sure to fill the entire hole to avoid an air bubble. The pic below is from the West System website. Do it similar but make sure the epoxy goes to the bottom of the fastener.
Advanced fastener bonding
For greater strength and stability, drill oversized holes to increase the exposed substrate area and the amount of epoxy around the fastener. If the fastener/hardware can be clamped by other means, the oversized hole can be extended to the end of the fastener.