Auto body repair & detailing: Paint Line Blending, paint line, adhesive strip

Question
Hello William,
In the process of a full restoration my Dad's 62 Belvedere. He has decided to paint the undercarriage, engine bay, door jambs, and underside of hood and trunk with single stage urethane. The exterior will be BC/CC and the color is solid black cherry. My question is how and where to tape/blend these areas so they don't "stick out" and have a smooth as possible transition. We will be painting all of mentioned areas this weekend and assembling the car, removing from rotisserie and painting the exterior complete. Any advise would be appreciated.
Thank You,
Jim

Answer
If you paint the underside with single stage, and the exterior with 2 stage- especially if it's  a metallic- you will regret it. I would base- clear the whole car. As far as edges, you need to roll back the tape- meaning mask to within 1/4 inch of what you are prtecting, and then follow with a line of tape that overhangs the edge by half it's width. Then, roll the edge bac into the jamb area. This creates a smoother transition than a tapl line. The trick is to not get any sealer into the roll back, it will leave a discolored line. It takes a lot of patience. There is also foam masking material available from 3M- kind of puts you to mind of cheap stick on window weatherstrip. it works good, but takes practice to master. You want to put it farther down into the jamb otherwise it's adhesive strip will leave a hard edge. Hope this helps. Bill