Hi BO,
When I was researching these tires, Duravis R250 and Michelin XPS Rib, both tire manufacturers stated that these tires were not suited for use in freezing or sub freezing temperatures.
I inquired as to why these tires were not suited to freezing conditions, the simplified answer I received was lack of traction in those conditions.
That being said, if one was to use these tires in freezing/sub-freezing conditions, there would be a dramatic loss of traction. That being said, in the case of a trailer, when the trailer brakes were applied, or when cornering there would a huge increase in the chances of jack knifing the trailer as the tow vehicle provided stopping power and the trailer brakes would have locked the wheels, and when cornering the trailer would experience a snap over steer.
Having said all of the above, I'm not that concerned about the freezing temperature limitation as 99% of my towing is in above freezing temperatures.