http://www.ripmax.com/item.asp?itemid=T-TL02&Category=130
I bought some the other day, not all that easy to use (to get straight) and I'm not entirely convinced it will stay on as well as the manufacturer claims (not on my paint surface, and getting wet anyway) but I think a couple of coats of matt or satin clear over the whole thing should seal it - and I could never get as good a result with paint, the one I used is only half a millimeter wide!

Mick,

Used the same 'trimline' on this replica Veron Police Launch. Bought mine from Model Dockyard.
My thoughts on using this product were identical to yours. It is more effective (and thinner) than car pinstripe tape.