Alan Holmes wrote:
[...]
As has been suggested in another post, get a cover for the van if cleaning
it is too much of a problem.

On this subject, while I have no experience, I wonder if the OP doesn't
want the tarpaulin look: I could see why. So, if the caravan isn't used
too often, how about a neat sheet of black polythene cut to fit the
roof and stuck on with that "outdoor sellotape"? That would be
unobtrusive and protect the worst-affected area..

--
Mike.