I never had an airbag in there Tibs
Mowog it's not actually hinged as such just yet, it more 'suspended' on a piece of fairly sturdy wire.
I drilled a hole into the side of the blank, threaded a bolt through it and used a nut to hold a loop at the end of the wire. You can just about see it on the side of this pic:
Essentially, I just cut down a car washing sponge to measure and roughly cut a couple of holes into it.
As said, it needs refining but the idea works ok