Cover it. Single digit temperatures won't kill a VFT, but freezerburn (dehydration) and repeated freezing and thawing might. Cover the plant (with clear plastic) so it doesn't lose too much water to evaporation, and try to keep the pot protected from direct exposure to moving air. It's rapid changes in conditions that you really want to avoid in this situation, so people often bundle their plants together under one tarp so that they share their bodily heat, and then wrap a few tarps around the outside to give the outermost pots a little extra insulation. If you're still concerned, you can pile up some leaf mulch around your pots for even more insulation after covering them (make sure not to leave a bunch of mulch in the water tray, as that will slowly fertilize your plant and VFTs aren't fond of that.) The most drastic technique for this purpose is to dig a hole in the ground and place the pot in the hole (make provisions to allow water to drain out freely so that your plant doesn't get a bunch of nutrients via the soil) and then cover it with a tarp, so that the warmth of the earth keeps the roots from freezing hard. I suppose you could also get yourself an insulated cooler and just stick your pots in that - you could maybe use packing peanuts or foam rubber to fill in the gaps between the pots. Remember, though, that the most important part is to loosely cover the top of the plant to slow air movement, as VFTs take much better to freezing than they do drying out.
~Joe