Do I need to add a circuit breaker to the outdoor panel that powers my RV?
Yes, you'll want a 30A breaker just to protect the RV.  

Breakers protect wires.   In the case of an RV, the internal wiring system is built to withstand onboard loads demanding 30A.  But if an onboard load has a problem, or if the wiring has a problem, and it suddenly starts pulling 100A, the RV depends on that external breaker to trip.  Otherwise you could have an RV fire.  

Even if the RV has a little subpanel on board, most likely the subpanel is "oversubscribed" and it'd be possible for all circuits to run at max, trip no RV breakers and pull considerably more through the internal wiring between the panel and the shore power connection.