Thanks for your responses.
I did use 1" Stainless Steel self tappers and I was able to locate the square framing using a stud finder and the old "Knock Method". Bracket is mounted.
I covered the entire back of the 1/4" thick bracket with Butyl tape, and after mounting I used silicone around the perimeter . I also looped the cable downward before feeding it through the hole to the interior kind of like a J-trap so water would not try to follow the cable directly inside.
Thanks again for your help