The above is a cross section illustrates the proper mounting of a cleat, the same principal would be used with any piece of hardware. Locate the hardware where you want it. Think about how you'll be using it and whether it might interfere with movement or other hardware. Mark the hole locations. Drill the holes, matched to the fasteners you are going to be using.
Most decks are a sandwich of fiberglass, balsa wood, and fiberglass.
This is for wiegth savings while still being strong. Therefore, after the holes are drilled I take a nail with the tip bent at a 90 degree angle and dig the balsa core out all around the hole. After the epoxy has cured re-drill the holes. They drill out easily and provide a pilot hole. Next, cut out and drill a wood backing plate.