Don't fill the water as you mentioned but we carry bottled water and wipes, we use the toilet holding tank as necessary, we travel with the heat on low perhaps 55 degrees and turn it up when we enter the trailer. Brad will be leaving Michigan for New Mexico on Wednesday. Stopping where there is electric for the night or using 12 volt
mattress heater pads for a short time to take the chill off or hot water bottles will warm bedding. Bring winter shovel, emergency food, water, and clothing and blankets in the truck with you. Drive till you get to where its warm or until you are at your destination... just like winter tent camping, only better????
We did go to Grand Canyon one January without running the heat while traveling. The bed was SO cold like a slab even doubling up with full outdoor winter clothing and covers, brrrr.