The first step is to only drill a "pilot" hole which should be less than half the diameter of the final size hole. After the pilot hole drill the actual size hole but make sure the depth of drilling is 1/4 inch less than the length of the screw being used. Dry fit the bracket using a smaller diameter screw to satisfy yourself this is exactly where you want the bracket to end up. Now fill the hole with a silicone exterior grade caulking and using the final screw(s) install the bracket.
Dennis (cut2it)
C&onstructi&on C&onsultant
Over 40 yrs. as General Contractor for new const. & remodel - retired with time for you.