When I winterize I remove the batteries and unplug the trailer from power. I do cover with an RV cover and I feel this is a great way to save the outside of the trailer and roof. I close the trailer completely leaving no open windows or vents. I use 2 dry-z-air refillable packs, one in the kitchen sink and one in the bathroom sink. I check the trailer a couple times through the winter, empty the water in the sink, and refill the crystals. I have yet to see any mildew or anything in my trailer - I live outside of Seattle - very damp area in the winter. Moss grows on the north side of your trailer if you leave it uncovered...