Well, your not exactly losing energy while changing it from one form to another.
In a heating system for houses or trailers, you're giving up all the energy to the surroundings and enjoying the benefits of the process. Your electric cube heater is giving up 100% of the energy you put into it, to the outside surroundings. You are just making an inefficient delivery system to the surroundings by delivering it to the interior of your trailer instead of just running the electric heater outside.
All heating systems lose all of their energy to the outside, eventually.
Your cube heater is fine as long as you have a power source for it. It's not really comparable with a propane
system that will run while off the grid. Propane
allows us to camp in cold areas, without shore tie and without running a generator
There are many ways to deliver the heat from a propane source to the interior of a trailer or a house. Most of us have a forced air system that blows hot air into the interior. That requires a loud and power hungry fan in addition to a propane burner. Another delivery system is to do what I described in my earlier post. Circulate warm water through tubing in the floor, from the water heater. Radiant heating. The advantages are: one less propane appliance, less noise, better comfort and lower power draw.
But if you are connected to shore power and it's just a bit chilly some morning, the cube heater can take care of it simply and quickly too.