I I have an outside weather proof receptacle that's 120V for an RV. It tripped when it rained so I unplugged the RV from the outlet and reset the breaker. It held in the on position and I plugged the RV back in. Everything is off in the RV. But the circuit breaker trips and will not reset and hold with the RV plugged in. Does it need to dry out before using it? Or might something else be the problem?

Is it a GFCI outlet? The problem would appear to be in the cordset to the RV. Have someone check for cuts or shorts to ground.

Agree but let it dry over night before you put too much time into it. Also try another cord maybe connected to something other than the RV.