You should crack some vents and windows to get some air flowing through. I know you don't want to let cold air in but moisture in the air needs to get out somehow. Unless you have rigid foam in the ceiling cavity, I think you're more likely to have condensation problems than a roof leak, esp. being in the PNW.
Cooking, showering and bodies all release a lot of moisture into the air and it will condense on colder surfaces. Unfortunately, the way RVs are built, what is essentially a vapor barrier, is on the wrong side of the insulation and moisture will get through to the cold roof and exterior wall surfaces and condense if its a batt type insulation. Can't see on the Thor website what insulation type is in the ceiling.
You could look at getting a dehumidifier. A hygrometer like this one at Walmart would be good to get to see what your relative humidity level is.
Indoor Hygrometer With Comfort Scale | Walmart.ca