How are you storing it? Or is it in use at this time?
I'm in WA State, so it's a bit wet up here.. :)
I store my rig with an Adco cover on it and leave the vents cracked just a tad.
I also keep a couple of driz-aire things in the rig and check them about every couple of weeks and they always have that gooey liquid in them and I refill and repeat.
Never any moisture or mold in the rig.
While in use, it'll get some condensation on the windows, but I still do keep the vents open a tad even if I need to run the heater.
Key is letting the moist air out as much as you can.
Or you have a leak that is not an obvious one... :)
Good luck! Mitch