Flames

In general, polyester fiberfill (available at craft and fabric stores) is much more convincing for rendering smoke and flame than cotton. It's easier to 'sculpt' and color evenly, and can be drawn out for a less 'chunky' look.

I'm supposing there are tutorials on Youtube that might help.

There are modelers who put actual flamethrowers on their models.  On a plastic model it would look really cool, for about 20 seconds.  

I had the same question a few months ago. Various ideas were offered, but I used some decals on clear plastic................

I should have cut the plastic closer to the decal perhaps.

PatW

I had the same question a few months ago. Various ideas were offered, but I used some decals on clear plastic................

That's a really clever solution. Well done!