Originally Posted by pmsherman
Your calculation for AC costs would be accurate if the compressor runs continuously. If you assume that it cycles off, especially at night, costs will decrease.
The biggest problem when using electric space heaters (note plural form) is finding places to plug them in. My 2011 Georgetown has almost all of the AC outlets wired to a single 20A circuit breaker, making it impossible to run two heaters at the same time. The only outlets that are on a separate breaker are the three GFCI protected ones, two at the sink and one in the bathroom.
One way to improve efficiency of heating, especially at night, is to close all of the slides except the bedroom. This cuts the surface area that radiates heat and makes it easier to warm the inside. I also discovered that the engine run AC/vent control needed to be set to "Max Air" to close the outside air intake. This is an electrically controlled mechanism in my Georgetown and operates with the ignition switch off.
If you don't have double pane windows, bubble foam insulating material over the windows will also make a good improvement.
That is why take. Extension cords you to plug into pedestal. I use one of those water weines cut it to length then split it and when I run the cord through window it seals it. I also use them cut pieces about 6"n long 45 them and piput them on corners of slides saves head bumps.