That's not an air bag. That is a variable rate, air adjustable bump stop.
I remember a guy in high school had a Dodge Challenger, actually a rare car because it was the slant six. He had it all badged up as one of the Bad-assed big block cars all jacked up in the back with N50's, you know the typical 70's kids hot rod. His solution to jack it up in the back........2X4s! He had 2 pieces of 2X4 between the springs and frame. I never rode in it but it must have rode like a boxcar.
Dave & Kandi & Indica the Chorkie pup "Big Blue"
2001 Holiday Rambler Admiral 30D w/ 2nd slide
2000 P32 7.4 4L80E wide track J71 18/21K