Thanks for the shout out and good luck with your edit!
I like the idea of the gas, at least is some limited capacity (and using only existing scenes). I liked NeverarGreat’s idea of introducing the gas concept through Leia’s dialogue with Threepio. If I had the skills I would show the thick mist that NeverarGreat describes, but just before their capture I would have it quickly dissipate with an accompanying sound effect or a ventilation system kicking in.
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”.