You probably have a 50 amp service on your RV.
If your cord is 40' long and the cord is #6 AWG wire and you have both legs at 50 A, very unlikely, you will have a voltage drop of 1.58v. Thus each leg will have 1.58 x 50 watts = 79 watts. So in this very extreme case you will have 158 watts of heat.
In real life you would have far less current and only a part of your power cord coiled up so the power dissipation would be much less.
Edit: Depending on the on the phase difference of the 2 legs, the power could be much less.
