Of all the jobs I don't look forward to when painting a model locomotive, it's got to be warning stripes on the ends known as "wasp stripes". They are eye-catching (obviously) and yet fiddly to get right.
I've tried various methods over the years. For the G1 Class 14 my method was simple - hand them over to my Father and get him to mask the lines. This wasn't laziness on my part, it's just that to get them right takes time and that was something I didn't have thanks to work commitments.
My plan had been to cover the entire door, draw the lines and then cut away the unwanted masking. He cut the tape into strips and carefully stuck them to the yellow painted parts.
All I had to do was paint the unmasked area with some Humbrol matt black and carefully peel the tape away. The results look pretty good I think.