Why do you have the trailer plugged in to power? To keep the fridge on so it doesn't get mold?
Winterize, open the door to the fridge and freezer, drain any water, etc. then you won't need the extension cord. You are using a temporary extension cord for a mostly permanent power source, that's a good way to start a fire. I have a 30AMP pedestal right next to my trailer and I still winterize and leave it unplugged for the winter, no fire hazard, no issue of burning up my batteries due to a bad charger, and no warm place for the mice to nest.
Good Luck with your power problem, sorry I couldn't be of help.