EstorilM,
If it's only going to drop down into the mid-20's on occasion, I don't think you're going to have to worry about pipes freezing IF you're going to be keeping the inside of the rig at habitable temperatures during the night. Especially if your daytime temps are consistently in the high 30's and above.
There can be other factors which come into play such as being in the shade so the daytime sun doesn't warm the rig, or persistent windy conditions.
There is one thing you have to be aware of if you use electric space heaters inside when it gets very cold outside. If the electric heaters keep it warm enough inside so that the furnace doesn't kick in, you could have issues with the pipes freezing. You can either play games with the thermostat settings of the furnace and electric heaters, OR, on those nights when you KNOW it's going to be well below freezing, let the furnace do the heating.
I, too, generally try not to use propane for heating unless necessary. I have purchased a couple of 200W space heaters (like
this) and a thermostat controlled power cord (like
this) and set the temperature on the thermostat to about 30 degrees. I put one heater in my water bay (water pump & dump valves) and another back near the freshwater tank. In the "old days" LOL you used to be able to hang a 100W incandescent lamp in the water bay to provide heat. Those bulbs are getting harder to come by, PLUS they can burn out or fail. For the peace of mind, I prefer the small personal space heaters instead. I believe them to be more reliable, albeit at a higher buy-in cost.
I often keep our rig "ready to roll" as late into the season as possible, sometimes even after the first couple of snow falls if I think we'll be able to get away. With the above system, I have had no issues with any water freezing when the temps drop as low 15 degrees while we're inside the rig being heated with electric heaters. If
it's going to drop colder than that, we do have to run the furnace, or it's likely the water will freeze in the pipe from the water tank to the water bay. (Never had a pipe burst, though, just took a while of running the furnace to get the water flowing again.) ONE of these days I'd like to either put heater-tape around that section of pipe or another portable space heater in that area...but it's not really much of a priority at all, since now I know to just run the propane as the temps head to the single digits. Plus, it would be a pain to get to! LOL
But from your description of the conditions, I don't think it's going to be too hard to keep everything working.
Good luck,
~Rick
