The FIRST thing you do is disconnect the LOAD side of the GFCI. See if it trips. If it does, then that GFCI (new) is bad. How many wires to you have on the LOAD side of the GFCI? If more than one Black wire, disconnect one set of the Black/White wires and leave the other connected and test again. If you have NO TRIP, then the other set has the problem. If you have just 1 Black/White wire on the LOAD side, you have to go to the other GFCI controlled plugs and disconnect them ALL and then see if the TRIP goes away. If it does, you reconnect until the TRIP happens. Odds are, EACH controlled outlet will have 2 or more sets of wires at its connection. Now, for the OUTSIDE outlet. The only sure way to verify and really test is to pull it out from its receptacle and verify no moisture OR corrosion from moisture. Remember, a GFCI measures the IMBALANCE between the WHITE(neutral) and the BLACK (hot). When imbalanced(Short) it trips the GFCI. There may be GFCI controlled outlets you do NOT know or see on your RV. You have to find them ALL. Doug