Living in California we don't experience high levels of humidity or rain so I'm always curious to read the post from folks in areas with lots of rain and high humidity.
It seems folks who live in these areas use dehumidifiers either electrical or powdered type to keep the humidity low inside their RVs while stored between trips.
I remember one story where the RVer thought someone had broken into their RV and scattered flour all over the inside...every surface had this fine white powder. It turned out to be mold. Their dehumidifier had stopped working and the mold grew on all surfaces in a week.