Your niece and her husband are in good company. People tend to be "out of sight out of mind". It's amazing how many posts there are come spring about "I took my RV out of storage and the wall/floor/ceiling is soft".
I always recommend that RV owners check their campers after the first rain of the season, and again after every major storm. Leaks happen. This lets you at least throw a tarp over it until you can repair the leak. A leak caught early is an inconvenience. A leak not caught is a disaster.