I always use a mild abrasive like Brasso or toothpaste. Obviously if the scratches are deep, then don't attempt it with those things. You could use the pigmented car polish that includes a same colour crayon. Rub the crayon across the scratch to fill it, then apply the polish to flatten the crayon filling and buff up as normal. I hope you are able to sort it out. The Brasso treatment works on the windows too.
2010 Kia Sorento KX-2 2.2 CRDi Auto / 2013 Elddis Avante 574
Be careful if you use any kind of abrasive polish, e.g. Brasso, toothpaste, T-Cut, Jiff or Ciff (or whatever it is called theses days). The finish on the aluminium on the sides of caravans is "printed" on rather than sprayed on and is only microns thick. It follows that even a careful wipe over with an abrasive such as those above, is going to remove some of the surface finish eventually. Having said that, I have used Ciff on the dreaded black streaks on the odd occasion to remove scratches. There is a product on the market called "Silky" which is available from caravan accessories shops. It is a non-abrasive compound and I have used it to remove very light scratches. It is brilliant for removing black streaks.
As the problem is caused by trees overhanging the lane, the situation will only get worse as the years go by and the trees grow. Is it possible to trim back the growth so that the caravan doesn't get scratched? Or is that impractical?