You don't state what chassis you have, but my Holiday Rambler with a Freightliner chassis exhibited a similar problem. Turns out that there are 2 circuit breakers located just above the frame rail on the passenger side near the engine. When you draw too much current, these breakers heat up and open up. In a minute or so, they reset, leaving no trace of what happened. This happened to me about 4 times, and HR was at a loss. A call to Freightliner quickly resolved the problem. One of the breakers had gotten "weak" and would open up, cutting the lights, engine, gauges, etc. It happened at night the first time, and I coasted to the side of the highway. I replaced that breaker and the problem went away.
Hope this helps,
Dick Lucas