I've been out cleaning with my
Butler truckmount all day in 10 degree weather(pretty mild day actually). I have even cleaned in 70 below weather. You can do it, you just need to plan ahead. Your water line will be the last hose to come in the house. Also, you might need to run the water through the line to heat it up before starting to run it in the house. In really, really cold weather is when you need to keep things moving. It is very rare that you will freeze up while cleaning.
I would definately keep the heater going in the van. If you can get it into a garage as well to help shelter it would be good. Eventually a heated and insulated garage might be a great investment. I have seen many truckmounts get froze up and it is very spendy. Most every connector ends up being replaced as well as heat exchangers, water pumps, you name it...if it freezes, it will break. Your scrub wands and cleaning tools will also freeze and ruin the valves.
You also need to consider that a few of your cleaning agents might also not be effective if frozen.
Give me a call if you have more questions. Being from Northern Minnesota and our family having been in the cleaning industry for 45 years, we have seen a lot.
Mark
Saiger
218-326-4736