Well, there may be a VERY simple answer to this situation.....
From your posting of 8-26, perchance was there a complete draining of the propane in one (or both) of the tanks? There is usually a collection of liquid(s) at the bottom of most tanks (teaspoons, maybe) that are usually undisturbed; they contain methyl mercaptan in a more concentrated state. When the propane (which is liquid) gets very near the bottom of the tank, the concentration of stink-um gets quite high, and the odor of the combustion gasses gets REALLY strong. If you smell that unexpectedly, simply change tanks.
Lemme know, please? I'm kinda surprised this hasn't been suggested before by someone else.....I've had five trailers, four of them Airstreams, in the last forty years, and it's been a characteristic of every single trailer when a tank runs out.