I bought a can of hammerite spray from Homebase - its the same colour as the dampers which is a bonus. Got rid of the rust and gave the dampers around 8-10 coats. I suggest getting some masking tape What do you means by "rough" though?
I used Hammerite rust removing gel and give them a good sanding down, then some primer and a good few layers of halfords spray paint (Renault silver) which turns out to be a nearly perfect match as the original, then I used hammerite lacqure as a final coat.
Within a couple months they were looking a bit run down again sadly.