One way to do 1/8" wide recesses commonly found on trim is to just use 1/8" wide pin striping tape. Just lay it in the groove and trim the ends. Looks good and is almost non-noticeable. (Is that a word?)
I agree with KosmicKuda's approach I used 1/4" pinstripe tape on my '67 trim and it layed on perfectly. No jagged edges, perfectly straight and smooth, quick to apply, etc...
