Normally I'm able to use a joint line or some existing line to indicate a panel line. When I don't and J&B is covering a needed door line I can scribe a line with an Xacto. This has to be redone every priming or the line will be lost. This is time consuming. I've also used jewelers saws; but these don't always conform to the lines of the body.

Just wondering if anyone else has a better way?

I would be interested in information on this as well.

I've used a razor saw to cut the line a little deeper so not to lose them in the painting process.