I used to lay my masking tape on a shiney surface (I used a book or something) and using a ruler cut down the length with a scalpel.. then use the CUT edge as the masking edge.
That is how I did it. I use vinyl now for most masked edges. If I do get a bleed then unless I am spraying chrome Its usually fixable without any real trace - just scrape it off. I am SUPER SUPER fussy about stuff like this - if you see an error on one of my shells then I would cry (and probably did).
