Protecting young trees from extreme cold

We have a cold front coming through here in the Okanagan, where usually our lowest minimum is around -18C, we are forecast to be down around -26c for two nights next week.
What would you recommend in terms of protecting young trees?

One tip I got from a nursery guy north of me is to cover them at night to keep them from losing radiant heat to the night sky on frigid clear nights.  Just a thin sheet or something does the trick. It's not for insulation, it's to block the sight line to the sky.

I take a hands off approach to frost. My basic attitude is that if cold is going to kill a tree, then it might be better if that tree isn't taking up space on my farm.