Extreme temperatures, like youroo stated, winterize and camp without running water or using the holding tanks. Filling and using FW like was mentioned is good if milder weather; as well as, attaching dump hose only when you need to dump and store it dry. If you have tank heaters, don't fill the tanks all the way up; they won't keep a full tank from freezing as easily as they will a partially filled tank.
If you have shore power use electric heaters as much as you can... burning LP either in the furnace or stove / oven creates massive amounts of condensation inside. Cracking open a ceiling vent and if needed, running the fan will help with that.
Some folks put a small electric space heater in the wet bay / compartment of 5ers and MHs. Light bulbs can melt plastic and make a mess. On a travel trailer, it might be possible to place a space heater in the area between belly pan and floor, but I would put a remote temp sensor in there to know whats going on and be able to turn it on and off as needed.
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