I've planted several first-year figs at Thanksgiving in Zone 6 and then pinned them to the ground with full bags of compost. I know that many fig growers will dispute the wisdom of this method, but I've never lost a tree. The compost "blanket" allows the heat of the earth to protect the young plants from freezing, even in brutal winters like 2013-14 and 2014-15. I haven't had any problems with rot from condensation on the plastic, I believe, because there is no air space between the plastic and the ground so no condensation forms. An additional benefit is that the mass of the compost tempers daytime temperature swings, so trees don't heat up if you get a couple unseasonably warm days in Feb. When Spring comes (usually mid/late April here), I split the bag and empty the compost around the tree it protected through the winter. Easy-peasy. Good luck!