Important question, do you have an LPG detector in your Airstream? And if you do, is it working?
I ask this because if you had propane leaking to the point that you could smell it, then the LPG detector should have gone off as well. NFPA 58— and by extension the fire codes of 49 of the 50 states that have adopted some edition of NFPA as the basis for their own propane gas codes— requires that the odorant added to propane be detectable by smell when the propane concentration reaches 20%
of the lower explosive limit. Of course, not everyone's nose is the same, and smokers in particular might not be able to smell propane until the concentration is much higher.
Anyway, your LPG detector is supposed to sound an alarm when the concentration of propane in the air reaches 10%
of the lower explosive limit. In other words, unless you've got the sensitive nose of a perfume maker, the LPG detector should sound an alarm long before you could smell the propane.
Which is is pretty fair indication that the smell you smelled was not
a propane leak.
The sulfuric acid smell of leaking battery electrolyte has nothing to do with the electrolyte expanding with altitude. Otherwise airplanes never could have used wet-cell batteries before other types of batteries were invented. Airplanes reach higher altitudes and stay there longer, and if they lost acid due to electrolyte expansion at high altitudes every plane would have landed with ruined batteries and acid-etched wings or fuselages at the battery location.
However, it is possible that a battery leaked because it overcharged. When a 12v
wet-cell battery reaches 13.8 volts or higher and stays
that way, it will boil, and there will be a distinctive acid smell given off. This normally happens when there is one or more bad cells in the battery, and the battery will typically show signs of bulging or other damage to the battery case.