Your Montana is rated to zero degrees. Keep the furnace running, unhook your water hose and drain it (use your fresh water tank on board and water pump).
If you have a water line under your slide out for an ice maker in your refrigerator, you can shut the water off to that line (usually under the kitchen sink), and open the low point drain for that line (usually right under the sink under the trailer also), and drain the water line going to the ice maker. Once the freeze is over, turn that water line back on.
On mine, you can see the water line running under the floor on the outside of the slide. It's a flexible hose.
On mine, here's one of two cut off valves for the water line running to the refrigerator. It's under the sink and T's off the water line running to the kitchen sink:
And directly under the kitchen sink area, outside, under the trailer, is a low-point drain JUST for the ice maker line.
Even if ALL the water does not get drained from this line, removing the pressure from it and draining is down will give enough room in the pipe, that if freezing still occurs, there is room for the ice to expand and the line won't get hurt at all.
That is really the ONLY thing you need to be concerned about. Other than that one water line, your camper will do just fine to about zero degrees provided you keep your furnace running. It HAS to stay running to blow air in the underbelly.
Just an FYI.... if you have the ice maker, you'll also have a second shut off valve. It's the small line that actually attaches to the refrigerator. These are located in different places in every camper. Some are inside cabinets, and some are more easy to access. But that second valve is inside the camper. You want the one under the sink shut off and drained from there.
