Storage covers and damp

Have recently had my van service and damp was picked up. Fortunately this was just before the warranty expired so all covered and no cost to me. However next time I won't be so lucky so wondering whether purchase a cover would help to reduce the chances of damp in the caravan or not?

Have been looking at pro-tec and specialised cover to and would be grateful for opinions on whether buying a cover for winter storage would help reduce the chances or damp