I wouldn't be too worried about the cold, other than possible condensation. I'm not sure a weatherproof box would really help with that, but since the device is passively cooled, that might make the heat problem worse in the summer--and at that temperature range, heat might be more of a concern. Here is a thread where you can find some speculation on this topic:
That being said, the hub doesn't have designated operating temperature, so most of these are just best-guess guidance based on similar electronics. You won't necessarily for-sure fail in either scenario. Depending on how close the barn is, you might be able to make the traditional Zigbee or Z-Wave mesh work with devices in that location (presumably you also have a hub in your home?), but at longer distances, that becomes less practical.
Here are some other threads you can find on temperature in case you are curious, though again most is just general commentary since there are no guaranteed specs for this:
