Don't do it ! Buy a piece of starboard and cut it to size and glue it to your transom. Then drill the holes into the starboard and not your boat. Now for the hole you have to make above the waterline for your cable just coat the inside of it with epoxy to water proof it.
The location is good. You can either drill into the transom and use 3M 4200 on the screws or do as Roger says. They do sell a pad called a transom saver that comes with adhesive to attach it.
Tghanks Roger.
Clicked the link and read up on it. You had stated " Buy a piece of starboard and cut it to size and glue it to your transom" but the manufactrurers say don't glue it as it will not last.