Wash it weekly and come to terms with the fact that the car will look like poo 80% of the time. You can only do so much. It sounds like you have a grasp on detailing and the products to use. Just keep it up. Black cars are a full-time job.
To be honest, even when I know the car is filthy, it still looks amazing 10 feet out. And when the car is clean... well, you know
