truck and trailer total loss due to black ice

Glad you are both OK. We had a similar experience two years ago but fortunately was only the truck, I was not towing at the time. When it happens its all over before you can do anything, so I would say the only things you did wrong was driving too fast and not using four wheel drive, which is exactly what I was doing. Oh, also I got dinged for not having winter tires (with the snowflake). I thought my all-seasons were fine, but not according to the cops and insurance company.
I still got a new truck but lost my no-claims bonus.