The wall mounted indoor propane heaters work well. The link is an example but get a nice one with thermostat. Most do not come with regulators so it installs into the RV propane system (rear of regulator) easily. No additional electricity needed either so...if
all else fails and you don't have any power...you will still have heat.
https://www.northerntool.com/shop/to...yABEgJRTPD_BwE