There are far more sources of unhealthy amounts of electro-magetic energy flying all around you everyday, then you could ever possibly get from the coiled up camper power cord. Cell phones, computers, TV's Microwaves, power lines, cell towers, unseen radio waves traveling through the air, etc. All of which you can get from just hanging out at home.
Regarding the use of an extension cord, sometimes you have to use one, just make sure you purchase one that can handle the full 30 amp load and you should be fine.
Model X19H Expandable
GMC Sierra Pick up
Been a camper since I was a kid, and that was a long time ago :)
From pup tents with no floors, to tents with floors and flies, to a pop up, to the expandable.