Mike,
Here in Missouri, near KC, I have all my fig trees in pots in a hoophouse (this summer I hope to have all in the ground). There is a divider down the length and the south side is heated. The older fig trees (purchased small in 2005 and 2006) are in the unheated north side where the lowest temp at pot level (foot and a half above the soil in a raised bed) was thirty degrees. All did well the last two winters. Those three are Italian Honey (24 brebas now), Violette de Bordeaux (40 brebas now) and Hardy Chicago (no brebas). Small trees from these varieties seemed to have survived (except maybe one honey) the cold side okay.
New trees from Jon last fall and another person last summer were held on the heated side until they went dormant mid-winter, (heat comes on at fifty degrees) then moved to cool side. All did okay until late winter when temps dropped into teens outside after the hoop had been heated to high temps during sunny days. At that time, Unknown Pastilliere suffered tip damage, but some very tiny brebas are still hanging on. No more leaf growth though. The others have continued to grow leaves. So, it seems the Pastilliere is more sensitive, but the others seem to have handled the change okay. Those other varieties are: Alma, Excel, Hollier, LSU Purple, and Nero.
King did not go dormant so is still on the heated side. It does not look as happy as the others with their new growth. The same is true of small plants from my older trees - Italian Honey and Violette de Bordeaux that were on the heated side.
I surmise that hardier varieties do better if allowed to go dormant rather than being kept on the heated side. And more tender varieties like the Unknown Pastiliere needs to be kept on the heated side but in the coolest location possible.
Elizabeth