We've been out in -10 C (15 F) overnight low a few times. Just set the furnace at 60 F and put a glove over the freshwater tank drain tap after it froze the first time. I was about to say there was no problem but we did get a cracked ABS elbow in a drain pipe from the sink that is under the floor with only the metal skin under it. Freezing water in the elbow might have cracked it. I now put several cups of antifreeze down the sink drain when it is freezing. I intended to get some stick on insulation to protect that pipe but haven't done it yet.
For the exposed freshwater hose, get a slip on foam insulator - inexpensive and very good protection.
