Lastly, I would explore explaining away the ineffectiveness of the gas in Jabba’s subsequent subtitles, something to the effect of “you must think us fools to try that old trick”.
I was thinking something more to the effect of “You fool. [Gas name] gas has no effect on hutts.” Then again, everyone around him was fine too, so I guess that wouldn’t work. That said, your line wouldn’t be any better, since it doesn’t actually explain why they weren’t affected.