If you are looking to keep your travel trailer in a lot all season, installing a 30-amp receptacle at the camp site is a useful option. This will allow you to plug the trailer in and leave it. It will also allow you to run all your appliances that run on electricity, such as your A/C unit when it is needed.
The National Electric Code (NEC) states that any outside receptacle must be "ground fault circuit interrupter (GFCI)." Subsequently, you must install a GFCI receptacle or a GFCI breaker. The 30-amp receptacle will need to be wired to a 30-amp single-pole GFCI breaker in the panel box. This will provide 125 volts to the travel trailer receptacle.
Run a 10/2 nonmetallic with ground sheathed wire from the panel box to the metal receptacle box at the desired location. Push out the round cut-out in the metal receptacle box, called a "knock-out" or "KO." Install a wire connector, push the wire through the connector into the metal box and secure.
Strip the plastic sheathing back to the connector and strip about 1/2 inch off the ends of the white and black wires using either a utility knife or wire strippers. Connect the white wire to the silver screw on the receptacle, the black wire to the brass screw and the copper wire to the green screw or the screw labeled "G" for ground. Push the wires back into the box, secure the receptacle to the box with screws and install the receptacle cover.
Turn off power to the panel box and remove the cover. Push or screw (depending on the style of your panel box) the GFCI 30-amp single-pole breaker into an empty slot in the panel box. Connect the white wire on the breaker to the neutral buss bar (with the other white wires in the panel box).
Push out the knock-out in the side of the panel box, install a connector, push the wire through the connector into the panel box and secure the wire in the connector. Strip the plastic coating off the wire, back to the connector and strip 1/2 inch off the ends of the wire. Connect the white wire to the silver screw on the GFCI 30-amp single-pole breaker. Connect the ground wire to the ground buss bar and the black to the brass screw on the GFCI breaker. Replace the cover on the panel box and turn on the GFCI breaker.
Test the GFCI 30-amp receptacle with a voltage tester and plug in the RV.