With a four season I would hope the design and layout lends itself to some protection of the water lines. As the saying goes “an ounce of prevention …” I would take it. Many of us have pex tubing that can actually take some freezing (not necessarily the fittings). My concern with borderline time and temps is the routing of the pipes. We have one pipe through the (outside) water heater access that is designed to take in air! If I ever build one I will trace the pipes with self regulation heat tape and insulation. Again speaking to borderline conditions…Hot water freezes faster than cold due to less air dissolved in it!