Caravan Covers - Pros and Cons

We are buying a new Bailey Unicorn Valencia caravan at the end of the month and would like to keep it in pristine condition. So we thought of a caravan cover, Bailey and the caravan club seam to endorse the pro-teccovers so what are the pros and cons? Do they encourage damp and mould in the caravan as the caravan is covered so moisture is more so trapped and ventilation is reduced.  Do they damage windows and are they a pain to fit by husband and wife. Opinions please.