I'm seeing similar temps here in central Arizona {at 5,000'} and the short answer is "Yes".
An occasional dip into the mid to high twenties is not likely to damage but... if it drops into the 20's and stays there for more than a few hours or so things will begin to freeze, and not in a good way.
I haven't had the need to blow out the lines and refill them with antifreeze but I do drain all of the water from the coach {and then drive it around for about 5 miles with the drains open and that chases most of the water from the lines down and out} and fill the traps {sinks and shower} with a cup or two and put about a quart in the black and gray tanks.
Our class C resides in the driveway and has AC power 24/7 so anytime the temps are headed south I can just run a small electric heater set to around 50 - 60 degrees. Opening drawers and cabinet doors help circulate the warmer air. Also the rig has tank heaters and I will turn them on anytime the temps are going to stay below 30 for any length of time.
We usually use our coach throughout the year but this is our first winter up at 5,000' so I will adjust the above as needed. good luck.
:C
