Back in the mid eighties when I painted my B33 tank I used gold vinyl strip and its still doing the job 25 years later!
However I've also seen a narrow blue vinyl strip you can use to mask up the lines you want and then paint between the tape and remove. This may be the answer for you...
Don't know if your bike should have a single or double stripe. I've seen some smart pics of triumphs with two lines but only ever seen single lines on beesa tanks. Be sure to post some pics.
I used white vinyl strip again a couple of years ago on a B50SS tank and laqoured the badge transfers and stripes (they have a george cross two tone all painted tank) and it looked very sharp!
Sadly the B50 had to be sold to fund my Road Rocket!