@hightor,
We certainly do need a root cellar! I googled my zone for advice and the styrofoam idea was commonly mentioned. I think I'm going to have to try it - there aren't many options. We get -20C to -30C for up to two weeks at a time, but this year, it was only -20c for a few days... so far. I think for those really cold nights I can go out with a few blankets to keep the extreme cold out... will keep you posted.
My onions are now about 6" high - too long and straggly, too early. <sigh>. But good news - some of my chilies are up - wonder of wonders.