On the first one, I used air-dry only. That was the BCM Jack copy that I built. Cerakote Sniper Gray. All I did for prep was etch the hell out of the upper and lower with some meanass shop degreaser - which ate annodizing. Sprayed it on, let it cure, assembled. It only takes 24 hours for it to cure enough to assemble parts. For application, I used a cheap, disposable air spray setup that I picked up at Ace Hardware.
The next two I did were bake-on Cerakote. I put those parts in the sandblast cabinet and took them to bare, silver aluminum. Sprayed, baked, and assembled as soon as they were cooled down. Those two were Sexual Chocolate and the Ghost Gun. For application of these ones, I picked up a decent (CHEAP!) airbrush gun at Harbor Freight.