Someone in another thread, recommended using Tamiya colored tape for the yellow stripes on iron bombs.
They make that tape in red also. I have seen it at Hobbytown and each pack comes with 4 or 5 different widths.
Just a thought.
If not that then try an Egg-o-rator. It might be hard to find this time of year though. It is a lathe like device used to decorate Easter eggs. Your tanks would be held in place by the rubber end pieces and the brush would go in a holder to the side. Then you just turn the little handle while slowly easing the brush closer to the part and VOILA!!!! Stripes on your napalm tanks!!!!
I also have seen pics where the napalm didn't have stripes at all. In fact, the bottom of the tanks were painted black to match the black undersides of the A-26K Counter Invader that was used on night time interdiction strikes.
Randie