It depends on what you want to run that GFCI too. That is where the 30 amp shore cord is junctioned and the Orange wire goes to the Breaker box. Now, you have a 30 amp trailer. IF you are going to be running the Roof AC, that will pull about 14 to 15 amps HI COOL. That leaves the rest of the trailer with 15 usable amps. The refer will pull 2.6 amps and the Power converter 1 to 3 amps depending on the DC load. That leaves you with 10 amps left. What type of appliance do you want to run with the extra outlet. If the roof AC is not going to be run, then you have more than enough current to run almost anything. The Microwave will pull 9 to 11 amps depending on its size. If you use a coffee maker or electric skillet--- 5 to 8 amps also. Hopefully you do NOT have a combo 120/LP water heater. They usually do not install a 120 type water Heater in smaller trailers. Doug