As long as you are regularly using it, you shouldn't have any issue. We live on the other side of the Puget Sound from the Olympic Peninsula, pretty much the same weather. We've found that when the van isn't being used, we either need to run the furnace (electric forced air Truma Combi) set on 48 degrees to maintain a constant temperature, or we need to run a dehumidifier. The day/night temperature changes will cause condensation, mostly on and around the windows and inside the fridge. Either keeping it a constant temperature or running a dehumidifier keeps it to a minimum.
Prior to the van, we had an all aluminum toyhauler, and the first winter after we bought it, we had a huge mold problem due to condensation inside. That camper had a propane furnace, so we started using a dehumidifier in it, and had no further problems. At least with it being all aluminum (even the cabinetry was aluminum) it was fairly easy to clean up the mold.