Hi
The main issue I have experienced has been the hose freezing to the external van ports. When I got to the job I spent time trying to get the water to flow. When it did start it was just a fine mist coming from the port but eventually the slightly warmer water in the tank unfroze it. Unfortunately, the water on the road turned to ice and I slipped on it and hurt my back - now I won't both to go out, it's too risky. One fall and a broken bone can put you off work for months - not worth it IMO.
On my sons van he has 2 external ports, an inlet to the top of the tank and an outlet from the pump. I suppose if you had the same you could cut a short piece of 1/2" hose, fit hozelok fittings on each side, couple to 2 van ports together, and slow run the pump while travelling to keep the water circulating, but we have never bothered.
Not cleaning the windows tomorrow is not a life and death situation.
Spruce