Yeah, I used TK 409s templates when I did mine. I printed out the templates, and slowly increased their size till it matched "actual size." (You'll have to make your own determination as to exactly how big you want them to be.)
Then I took a ruler and some blue painter's tape, and marked the basic rectangular shape of the stripes on the helmet, making sure to "burnish" down the edges of the tape really well with my fingernail. I then took a paintbrush and some of that Winsor & Newton's masking fluid, and painted in all the chips and missing areas.
To actually paint the stripes on, I used some Polly Scale UP Armor Yellow with a dense make-up sponge. I got some paint on the sponge, and dabbed it onto a paper towel to make sure it wasn't overly wet, then dabbed it onto my stripe templates. It didn't cover in one coat, but it dries really quick when you're doing such thin coats. It took about 4 applications overall to get it even looking. After it was totally dry (I waited at least 4 hours), I brushed on some red-orange pastel powder, making sure to make it heavier toward the back, and working lighter and lighter toward the front of the helmet. After I had brushed on the pastel, I removed the painter's tape and masking fluid, and immediately sprayed on some Testors Dullcoat. (Pastel will smudge
VERY EASILY unless it's clearcoated) I only had 3 tiny areas where the yellow had leaked under the tape, and those were carefully scraped away with a semi-used Xacto blade.
These are the results I got using this method:
