Stuffed with newspaper and masking tape, the coach body was treated to a couple of coats of Halfords white primer, followed by some satin clear laquer from the same source. This went well, and showed no significant sign of yellowing.
The results might have been neat, but looked a bit insipid. Something else was needed, so I took a deep breath and dug out my bow pen. I'm not a confident user of the tool, but reasoned that if I didn't like the results, the laquer would allow me to wipe them away.
As it was, a couple of lines down each side of the raised beading, carefully joined up so they looked like a fat one, went on pretty well. The thing with large scales is the lines are wide, and I'm not sure I could do them in one hit with the pen. Two passes seemed to work OK.
This still wasn't quite right, but rounding the inside of the corners with a brush, even if a long way less than perfect, makes a massive difference. At that point, I decided to quit while I was ahead. A bit of skill aquired, and results I can live with. That will do me!