I have seen several versions including this same formula, which I am a little nervous to try. Basically scrub your windscreen with the finest steel wool. Then use a product called Rain-X (several times), apparently Halfords sell it. Finally polish the screen with first a damp cloth (T-shirt) then a dry cloth (T-shirt).
I had not come across this before but it seems this is one way to clean an RV in America.
Has anyone tried this that I could trust?
Alan