Run an extra 15 amp power cord for the 3rd AC and plug it into the service pedestal. You can install a twist connector on the trailer exterior with a spring loaded or twist on lid. Then to route the power up to the AC, use a surface mount wire chase from LeGrande available at Lowes or HD. I used this to run 12 gauge romex from the AC in my toy hauler down to add an outlet to run an electric heater for cold weather. It was simple to cut a notch in the inside AC grill to run the romex and wire chase into the AC unit. Looks very clean.