High 20s is just below freezing, I wouldn't worry bec. there is enough residual heat being radiated from the trailer to keep things from freezing and if an exposed line does freeze it will only be for a short time and then thaw in the morning. It is temperatures below 25 for an extended period of time you should be concerned of.
2013 RAM 3500 Dually Longhorn
2014 Trilogy 3650RL, W/D, Onan 5500, 8000# Axles, IS, 960 Watt Solar, 6x6 Volt Battery Bank, Freedom SW 3012 Inv/Charger