For cowls, I either mask off the pinstripes, or use the Great Planes stuff...

For everything else though, I usually use my Top Flite stripe cutter. I can get a pretty thin strip of monokote without too much of a problem. I'm dangerous with a metal straightedge and monokote, so I try using the trim stripe cutter more often

http://www2.towerhobbies.com/cgi-bin...?&I=LXHZ33&P=0