Fuel tank painting.

Oil based paint to give a longish drying time. Then you can wipe off and repeat any errors. Wear cheap white cotton gloves from Boots so the back of your hand slides nicely over the tank.  Very long soft bristle brushes. I once used 2 inches cut from the beard of a friend's goat, wrapped tight with sticky tape.  Check YouTube.  Mark adjacent to line with chinagraph or soft pencil.  Some put lines (and transfers) on after lacquer.  If you do it yourself, you can always repair short lengths if they do rub off.  Test on a biscuit tin before lacquering over oil paint and then you can decide.  Try and find a copy of "Radco...vintage motorcycle workshop", published by Haynes but out of print. Very therapeutic.  You will be much slower than a professional but not necessarily worse.

Or buy a Beugler lining pen. ("Pinstriping tool" in American speak)

Stick-on stripes originally. Come as both stripes on a roll so spacing between stripes is done for you. Then apply petrol-resistant clearcoat over.

As Stan says, using a petrol resistant clearcoat is critical on a petrol tank.  Oil-based paints take longer to harden, but I would trust them more.  Careful use of a hairdryer will help.  Not a heatgun though - too fierce! Stick-on stripes are best with clearcoat applied on top, but it might be worth giving them a test on a spare piece of metal in case the paint cause them to react.  No good using cellulose lacquers on them as the plastic melts!

Gone are the days when I could put 4 or 5 light coats of cellulose paint on a car in one day - outdoors in the sun!  The 6th coat was best applied a day or so later - depending on the temperature. All metallic paint finishes must have a clearcoat top coat or the metal flakes can oxidise.  It's also necessary to give it a full gloss finish.  Many solid paint colours will benefit from using a clearcoat for the same reason.

there are many clearcoat aerosols available. However, nearly all are NOT ethanol proof. I wish I knew which are the proven ones, but still searching!

    2K types are probably the field to be looking in. Then you have compatability with the previous paint layer…..

... either side of the lines I want then use One-Shot signwriters' enamel with a soft brush for the actual lines.