There are 3 areas to address: First, I use to have a TM cleaning company in the far north - cold and more cold. Oft times my van was outside in the winter. I used a radiator "Block Heater" (electric plug-in when the van was not in use). One block heater was installed in my slide-in unit. A second block heater was for my van's motor. The water hoses and wands were moved near the slide-in or brought inside if it was really cold (20 degrees below). Never had a freezing problem.
No. 2: I installed a second "car heater" (off the radiator water lines) for the back of my truck when driving. My van was always toasty warm. Also, I never worried about anything freezing in the back of my truck. Later, I installed a 25 gallon "water box" (for the high pressure water pump) and put the block heater in it - keep the interior of the van warm through out the night.
No. 3: During the winter - to maintain heat in the high pressure cleaning line from the truck to the house, I put the high pressure line "inside" the first 50 feet of vacuum hose (similar to most of the upholstery cleaning tools). Worked great! A little harder to coil up at the end of a job - large coils solved that problem. (did not use hose real)