What's the coldest we've ever washed a vehicle?
I towed a '54 Chev pickup to my parents' house on the West side of Wisconsin a couple years ago, and when we got into town the thing was covered with junk from the trip. At the time I think it was something like zero. We were able to get the junk cleaned off the truck, but the rinse water was frozen to the truck before it left the stall. I believe the ice came off in springtime.
As for the 'fleet', yeah, we pressure wash at the local car wash. Quick, and does a decent (not great) job.