I happen to be kin to some auto-painters. I've seen them use a product that was actually a pre-made mask for pinstriping. It went on just like pinstripping tape but was a bit wider. You pull off the top layer and it leaves strips of high quality masking tape on the surface to be striped. Paint between the strips of masking tape. When it dries pull the tape off and you're left with a nice clean uniform stripe. (or double or triple stripe depending on the pattern of tape you use) Several coats of clear can be used to "level" the finish so the stripe doesn't appear to be a ridge. I've even seen one of my cousins cut masks for special designs on a vinyl cutter and use them in a similar way.