Sheep dip folks,
Some of you have obviously NOT been at any of the ski area's here in the NW US! Over 100 units on any given weekend at some places. NONE of them are winterized! I drained everything in the spring, refilled with water come Thankgiving to spend weekends at the local area. It got down to 10F many times, 20-25F max during the day for a weekend, ie friday pm to sunday pm!
ANy way, for the temps the OP is in, keep the heat going, inside lines will be fine! If you are going to be in sub freezing temps a lot as I was, get rid of any drains mid stream in the main lines, as water will freeze up and you will not have water beyond this point! Their are some other things one can do to make things better per say.....Unless you are going to be someplace as noted, below for a day or three or more, get some 2-3' of snow on the rig over those 2-4 days......you are worrying about nothing!
Marty