How do you paint window trim by using rattle can and nothing else?
 

as topic ^^ ?

Very careful masking!

I'm sure they is various ways but why not try using the supplied masks with the shell, once the shell is painted go round the mask with a sharp blade and trim 4-5 mm (or however thick you want the trim) off the mask, remove the strip and paint ...

As per AndyP above, paint body as usual, trim area around window you want to paint, paint then remove rest of window mask.

note though you may need to mask off the other areas if you have say a white shell and want the window trim black to stop it dulling/discolouring the white, most opaque colours are usually fine as the paint is usually pretty thick with cans.

just test on scrap lexan to see if the colour will come through before doing.

Good look.
Graham