Granted, there may be something wrong with the power source, but why not run a second utility extension cord to the camper for the extra electric heater? Feed the wire through a hole in the camper somewhere, or though a cracked window if nothing else. Make sure the extension cord is plugged into a different circuit than the one your camper is plugged into.
I run an external orange construction style 100 foot cord into my camper for using an extra electric ceramic heater, or when using the electric frying pan, or the electric griddle (inside). This never draws power THROUGH the camper wiring.
In the mean time, consider getting your RV receptical switched over from your current 30 amp to a 50 amp and then get a good 50 amp RV extension cord to reach the extra 10 feet.
