Quite interesting, especially considering that neither propane nor natural gas has a perceivable odor.
The "rotten-egg" smell from both propane and natural gas is from an additive called mercaptan that is there just to let you know there is a leak. Otherwise, there is no other odor detection.
Now, to the smell from the H2. Do you notice it more when you let off the throttle and are slowing down? This is a good indicator of the converter. I will tell you that diff fluid smells nothing like the sulfurous smell you are talking about. Believe me, the smell is still in a couple of my shirts from Moab.