Well, making the hole in the inner B-piller was, to say it mildly, an absolute pain in pretty much any part humanly possible and loosing a more or less important body part is always possible till very very last second until the hole is exactly where it needs to be!
I can not make any recommendations how to go about this job… you are working in limited space, very counterproductive angles of sheet metal ( which is responsible that the hole isn’t really round from this prospective) and Home Depot doesn’t sell a StarTrek phaser (the extra small version) in their tool section!
And tomorrow …a little welding.. tube to flange.. 👍