Hi nueboy
You have so mutch right about wet soil , moisture and humidity.
What can kill a cordeline is that Moisture first and then frost.
I have a good mate in Loou in Cornwall. It`s rains there all the time.
And somtimes every kind of palms an yuccas spicises dies of wet soil an Mosture there
And a little reminder he says that frost is also killing at his place
So perhaps 3 month below cero and dry conditions is better than a temp going up and down from day to day. Spec. yuccas likes dry coold
John