With lows around 30 you should honestly be okay. Getting down to 25-ish though, that's when I would be concerned. Like someone else mentioned, let the pipes maintain a slow, constant drip. This not only relieves pressure, but brings in "warmer" water from your main water line. The main line is deep enough that it will never freeze, so if the water in your house pipes is at risk for freezing and you are slowly flushing it with warmer water, that should help.