Exterior outlets can be installed to provide 120 volt access from outside. For safety, exterior outlets must be the ground fault interrupter type (GFI), just like the exterior outlets on your house. These provide protection from electrical shock by automatically shutting off if abnormal current flow is detected.
Common mounting areas are underneath the trailer along one side, along the bottom rail of the exterior side wall and along the top rail near where the side wall and roof meet. Location of exterior outlets depends on how you will use the trailer. For example, if you plan to add an awning area to one side, you may need power for something under that awning, such as kiosks, sound equipment, outdoor cooking equipment, coolers, etc. If you have lights suspended from the top support rafters, high mounted outlets near the roof may come in handy. Outlets can also be wired through an on/off switch if desired.