[JRTJH]

I'd start by opening the roof vents (since the trailer is inside a building). Also open (very slightly) a window in each major part of the RV. That will set up some air circulation inside the RV. If that doesn't work, then consider a dehumidifier. There are "bucket air dryer crystals" that you throw away when they're saturated and electric dehumidifiers that can be set up to drain into the gray tank on the trailer.... If you have power on the trailer, you can always set one of the air conditioners to run on low and set at 78F or around that temperature. You'll have to experiment with your storage conditions to see what's most effective. That will help dry the air in the rooftop spaces as well as dehumidify the interior of the trailer.