HELP! Winter leak

I started getting the camper ready for our Spring Gathering in two weeks. As I just put it together last year, I kept an eye on it over the winter. Apparently I didn't check it well enough. This is what I found when I looked under the matress.

I opened it up to dry it out in the nice weather.
Expert builders, I need your help. What can I do?





I opened it up to dry it out in the nice weather.
Expert builders, I need your help. What can I do?