Preventing black streaks

BanditMrP

I used search on the forums and got the following:

Sorry, no pages or documents were found containing "Streak remover" .

So... What do you all use to remove black streaks from your caravan or motor home, and is there anything which adds a "streak resistance" to the van?

Any recommendations for best "remover"?

I've just washed the van and most of them were removable, but down the solid back of the van they are still there.

Thanks in advance