Get out a voltmeter and measure at your AC breakers/distribution panel. Take off panel cover, measure incoming feeds (left side bottom big wires on mine) then each of the smaller solid wires going from each breaker to the loads. If this all measures OK, my next guess is that you need to pull out each and every outlet and measure its wiring. I posted on the RV insulation displacement outlet connectors (think puny Scotchlock auto wiring connectors) in a thread about someone's microwave not working yesterday.
More examples of no quality assurance checks at the end of the factory production line. How hard would it be to simply plug in a monkeyface tester (3 LED outlet tester) into all the outlets before releasing the trailer for shipment?
