(machine just timed out on posting a most elequent response :cussing
Check out the link I gave you for primer durability.
Water based (brush on) primers just won\'t be as durable or hard as enamels no matter if you airbrush them or paint them on with a brush.
Enamel primers leaves you with either automotive or something out of the hardware section (rustoleum, etc.). In any case, you will have to thin or reduce to get something you can shoot. Reducers for enamels are generally toxic, booth or no booth. If you shoot anything with Tolual or Toluene (also known as methylbenzene or phenylmethane) you should have a NIOSH respirator for oganic vapors and a face shield. I doubt you will see any, but if you use anything that has MEK in it, a full suit is just about the minimum. If you are a true paint shop, you will be held to higher standards than us meer hobiest.
For me, if I want a real nice layer of primer, I\'d get Tamaya. General play/tabletop minis get Krylon. Armory has had so many quality control problems, that I\'d never let that stuff near my minis.