IT depends on many things.. But the biggies are
How big is the cord
How tight is the coil
How many "Layers" is the coil
How much current.
I too have never seen a fire from one that I am sure of (I have seen many fires where I do not know the cause, and many where I do, I mean I lived in Detroit after all).
But I have drawn say 5 amps off a 12GA cord that was coiled and though it did not melt and it did not catch fire.. I could not hold the coil in my hand, and I can generally hold things others find too hot to handle. I mean it was alarming and I was no where near the cord's 20 amp rating.
Had I drawn more power I'm sure there would have been issues.
Bottom line, a single turn will likely not cause a problem even two turns.. And most RV cords are heavy enough and short enough that 3 turns is not likely.
