It also depends on how long you're out in freezing temps. For 1-2 days, you probably won't freeze a 5 gallon jug completely unless it's REALLY cold and you're storing outside of your heated area. Otherwise, there are a few tips that work:
1. Every night, pour some water in your pot before going to bed. This way, you can thaw it on the stove and make coffee, or defrost other containers/food items first.
2. Pour a liter of boiling water into your water jug before going to bed, and insulate it with clothing, towels, etc. This will usually keep it 90% liquid until morning.
3. Keep the container inside the cab while you travel. Another variation I thought up would be to place a heating pad from the drugstore on your jug and run it from an inverter while you're moving. 80 degree water will take a LOT longer to freeze than water which is already 35.
4. Do what we did this trip: Camp next to hot springs! There's nothing better than an unlimited supply of 105 degree water for defrosting things!
Arclight