We like to use the campground power to run out electric heaters as well. The best thing we came up with was to run a second extension cord out to the pedestal and plug into the CG 20AMP service.
This allows us to run the electric heaters off their breakers verses the RV...
The problem may be to find a spot to run the extension into the trailer without leaving an open weather hole somewhere. I was able to come thru my storage bay door and up into the bedroom thru the dirty clothes chute on my 5th wheel..
Using my off-road camper which is the trailer we use the most it is easy to come through any window flap...
Just a couple of thoughts for you..
Roy Ken