Used Autoglym caravan cleaner only yesterday here on site!😀
I'm banging on (a little too much) about the pink stuff as its not what you would normally think of, as in its not caravan/car related and I found it was more wiping than rubbing for application.
I do use Autoglym super resin polish on the van but it is a cutting compound so care is required, as I posted earlier I was worried about over use on the caravan as I have used the product on cellulose painted surface to polish/cut out orange peel.
The best ,the cheapest, and the easiest way to remove black streaks is an aerosol furniture polish. Spray on to van or cloth and wipe. Used it since vans had glass windows.
I like anything that doesn't have "Caravan" in front of it, usually cheaper.
For example we bought Caravan awning foam squares, when they needed replacing 2 years on, bought foam squares not related to "Caravan" exactly the same, almost half the price!