Run straight washer fluid, it won't freeze till like -40°. You'll probably go though much more washer fluid than you did in Texas. When the conditions are just right I go though a gallon of ww fluid every tank of fuel. When the road thaws from rising temps or ice melter after a snow the traction sand (now mud) flying off the road from anyone you get behind or who passes going the other way will instantly dirty your windshield. You'll learn real fast to keep your distance from the car in front of you. If you like keeping your rig clean you'll probably have to hit a carwash once a week or more in the winter. Vehicles in Montana tend to start looking pretty ugly in the winter.