We have a Protec breathable cover, some years we have used it and some we haven't because we have wanted to use the van in the winter, not noticed any difference apart from the van staying clean.
apart from anything else I couldn't do with the hassle of putting one on. In my storage compound there is one covered van in about 300 caravans. Having said that there are no trees or anything so doesnt get dirty.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.