....come to think of it, it just came to me that our manual car/truck wash (17 kilometers away) is heated in winter (auto open/close doors), and may be wide enough for dualies. Before we sold our Chevy Tracker, I used to use this manual wash to power wash the undercarriage and exterior during winter. I'd then use the compressed air fitting to dry out the wheel hubs, door perimeters and windshield wiper assemblies, then shammy off the exterior, all in the comfort of the heated bays. Also, the water coming out of the powerwash nozzles was HOT.
I brought our truck camper rig (2500HD SRW, 8-foot bed extended cab) into one of those bays during summer on one occasion, but I couldn't close the automatic door, because I wouldn't have room to power wash the rear of the rig. If you have a short bed truck, such bays could be a perfect fit.
So my thoughts are: try and find a winter bay-heated manual truck wash in your area, with doors that close. They MUST exist in your region. How could they afford to operate all winter without heated bays?
When we drive down to Florida for the winter, I always power wash the road salt dust off our SUV in DC (our 1st stop) at one particular truck wash with hot water power nozzles, just west of Andrews Air Force Base (on Suitland Parkway). From there south, there is very little de-icer on the roads because we plan our drive between snow falls, thus avoiding wet road surfaces.
Winter valves:
...we have winter valves on the exterior of our house, but I would never use them with a hose attached during most of our winters (the water would instantly freeze in the hose at the temperatures we have here all winter: 5F to -36F). If we have a short warm-up during winter (usually 1~3 days during the 3 colderst months over the 6+ month winter), I sometimes attache the hose.