Do the airbags in the coils rather instead of new springs with bags?
yes, air bags usually go inside of the rear coil springs.
Air bags are just that, bags, they are NOT steel.
They will tear, rip or leak, eventually.
If going with air bags, the use seperate air lines to each bag so the air does not flow from one bag, to the toher, when cornering. kinda defeats the purpose of an air bag when that happens.
air bags essentially provide an adjustable bump stump.
Think bottoming out your vehicle and the corresponding stiff jolt that would include.
air can be compressed. when compressed beyond beyond bags ability to withstand, it blows. just like a balloon.
air bags have a purpose and a function. but not the need all , be all, alot of guys think.
Get springs, real hardware, that serves the purpose, then add air bags to help them out, to achieve the ride you desire, when under a load.
doing this will insure your bags are never THAT pressurized and the springs will do the majority of the work, as they are designed.
Bags/Springs run about the same price.
I think springs are probably easier to install.
Luck
PS
Now, for the air bag fanboys, read below: