Try using a de-humidifier , get the 110 v one, then put in the sink so it can self drain. also leave a vent cracked open. You need a tiny bit of air flow, and the coach needs to breath a bit.
Or as a test get a few of those "keep it dry" tubs that CW sells, just remember that you need to set them in the sink(s) so they can drain into your gray tank & you won't have to empty them twice a day
An SOB called Foretravel