You should be fine if it's not combined with howling winds.
Got caught like this in Feb while camping on a warm weekend. Unexpectedly dropped to upper 20's and slight wind in the forecast. Grabbed a few of the thickest, fluffiest towels we had and wrapped the low point tubes and and fresh water drain tap & secured with bungee cords. Disconnected fresh water hose.
Checked in the AM, both low points were barely cold to the touch but the fresh water hose we'd left beside the trailer was frozen solid. May have gotten lucky, actually. Next time will just pop the caps off the low points and let them drain. A mere 5 minutes to prevent a crack is worth it.
And yes, most new trailers should have pex rated to 100psi. The fittings and valves, however...that's probably our weak points.
