If the corner store is still open, grab a few of those hand warming packs, wrap one or two in a thick towel and press it up against one side of the enclosure (on the outside). If not, insulate well, move them into a smaller room if possible, consider lighting a few candles while you're awake to keep the temperature up. It's certainly not ideal, but you'd be surprised what these guys are capable of handling. Don't take any risks with their safety or your own.