Place desired amount of onion and celery into a large mixing bowl. Add crabmeat, and sprinkle in a little bit of garlic powder. Lightly toss together. Add mayonnaise, starting with roughly half the container, and one scoop of sour cream. Mix. Add more mayo and sour cream until desired creaminess is achieved. Sprinkle Old Bay over the top of the mixture and refrigerate for at least 6 hours, if not overnight. Mix well. Taste for seasonings. Add more Old Bay if needed also. Serve cold.