Found the problem, and im glad to say its not the converter! I don't need any excuses to spend more money this holiday season.
The culprit seemed to be a loose ground connection behind the 12V fuse panel, which I assume connects to the trailer chassis. I tightened several connections and now everything works on 12V power. Its interesting that this can happen while the trailer is stationary and unused. My conclusion is that these parts expand and contract with the changing weather and things start to loosen up.
Now I can enjoy my weekend!