Someone recommended "fine line" masking tape, which is apparently more vinyl-like than the green 3M product I used. If I had it to do over again, I'd plan to just use vinyl striping from the get-go. I ordered the strips from Aerographics. The vinyl is very thin, and a little trickier to apply than a roll you could get at the auto parts store, but looks like it's painted on. I do NOT think it would do curves well unless it were a very thin line. However, if you wanted curved decals, you should talk to them. I only have good things to say about their customer service. My scheme intentionally has no curves. (Easier to paint and easier to repair.)
Edit: I do have 60' of 3/8" white striping left. Anyone is welcome to it for the cost of shipping.