the overhead lights are on the 12v
circuit, so their power is coming from the battery.
the 110v receptacles work via the circuit breaker panel. one of those circuits has tripped...or, the breaker that governs the circuit on which your external extension cord that is providing power to the trailer has tripped. (not hard to do with a long extension cord).
Its hard to tell if a circuit breaker has tripped just by looking at it. best to switch it all the way in one direction, then all the way back to the other to make sure its re-set properly.