Ive made these pictures excessively large to hopefully help you see whats going on here. And any airlines I have that are outside the car, or that squeeze through a tight space I have wrapped in a 1/4" ID rubber hose for protection.
Under the rear of the car (where the OEM muffler would be) the airbag you see in the picture is the rear driver's side airbag
Facing the same direction, just a little higher so you can see the air line. You can also see that my airlines are inside of a rubber hose.
The holes I drilled are 3/8" and the rubber hose fit absolutely perfect into them. The rubber hoses make a great seal so I don't have any issues with water getting into the trunk.
This picture is shot from way below so that you can see where I have put the holes, its easy to see where they are if you look at the OEM diff bushing.
And finally a close up of the lines going into the trunk