First I needed to be able to draw flames. Earlier attempts looked like crab claws. Maybe a bit of practice is in order.
Tools for the job include a fine tip paint brush, a Sharpie marker, and a single-action Paasche 200 airbrush. I found the Sharpie wouldn't write on plastic or paint unless you lightly sanded it first.
Using the Sharpie I drew flames on some junk box bodies by hand. This is looking a bit crab-claw like; after some practice I got a little better.
Once the shape was drawn in I went over it using paint. Acryic seems to work OK for this. But here's the best thing--using Acrylic, painting details over an enamel or lacquer color coat, it's easy to fix "mistakes" with a q-tip dipped in Windex, since Windex will take off the acrylic but doesn't affect enamel or lacquer color coat below.
Then I filled in the outline with some Jacquard color. Anything that "spilled over" the flame outline got fixed with Windex used as a thinner.
This is about the best I could do after an evening of messing around with this.
In general, flames are not easy to paint at scale I am finding. Things are just too tiny. The biggest issue I have is the pinstripe that goes around the flames. I know there is a way to do this because I see other modellers who have figured it out. But for me, the lines around the flames come out too thick, making them not look "scale". I got some extra fine Sharpee paint pens, maybe that will help. Stay tuned.