On some rigs the tanks are enclosed... On both of the trailers I've owned all plumbing was internal, no external save the waste drains and city water inlets and the fill spout on one (the other filled inside) But if your tanks are external then I would suggest carrying bottled water, INSIDE. Other than doing a full winterize, no special requirements
If your tanks are either inside or "Enclosed" then you are likely good down to 25 or 20 degrees so long as you run the furnance, You may open lower level cabnets to improve heat to plumbing in those areas (Under sinks and the like)
City Water hoses are out, and when you dump your tanks drain the hose (do not let it sit with waste water in it)
I did put some heat in the "Wet" compartments (Wet meaning the ones with tanks in them) I currently have most of a string of C-9 christmas lights in the main wet compartment (Has fresh water on one side and black/gray on the other) and 40 watts in the other wet bay (gray only) I have a few 100 watt bulbs I can scatter about too, as well as heaters