My TT stays drier inside when I not only keep the vents closed but also cover the TT with a plastic tarp and then and ADCO cover. The reason I say it stays drier is because it fills the DriZair's at about half the rate of allowing the RV to breath. Just my experience here in the NW. Your results in other parts of the country may vary.
A little heat and open roof vents helps to keep moisture out of the rig. Install vent hoods over the vents allows you leave the vents open even during rain. Of course in Astoria, you never get any rain!
I keep mine just above freezing. I heat it because freezing can make woodwork crack and because it's common for linoleum type flooring to suffer long splits (happened to neighbor) in both RV's and boats around here if they freeze.