If you live in a rainy climate, or are traveling through one, you have probably gotten those black marks caused from the rain running off the side of the RV or pullout.
First, elbow grease and any kind of all purpose cleaner won’t remove these marks. You need to use a car cleaner or polish in order to remove them. So unfortunately, this is one of those jobs that you won’t be able to use a household cleaner on, you need to use a specially formulated vehicle one instead.
Many RV owners sear by DriWash n Guard as their go to exterior cleaner for an RV. It is a bit pricey, but it definitely is good for these marks. If you are cleaning the entire outside of the RV, you don’t need to use it on your entire trailer or RV.
If you have any decals, it is always smart to check on an inconspicuous part first.
Others have tried using Mean Green and Magic Erasers too, but again, be very careful of the finish.
If you bought an older RV with streaks and you can’t seem to remove them, it could be that the RV was waxed, essentially sealing the black streaks in.