We very frequently use a Vornado heater as it does a great job of circulating the heat and keeping it constant with a thermostat. We don't even use the furnace until it gets below 35 or so. Of course the interior size of your unit is a factor. Space heaters cause a lot of house fires when improperly used but we even run ours all night sitting on a hard surface and completely away from flammable material. Most RVers run heaters to use the campground's electricity instead of our propane. I'm not sure they present any more danger than the furnace or water heater does.