Here's some tube strip masking templates if you want to cut your own. I made these in Adobe Illustrator from scratch, they are not based on any specific trooper or design. Print them out to size, then place them on top of sign vinyl, etc. Cut through the paper and vinyl (ideally without cutting through the vinyl backing paper) and simply weed out (remove) the inner bits on the vinyl to create the template.
You can use sign vinyl, masking tape or airbrush frisket. Use a sharp Exacto / hobby blade.
Here's how I paint them:
http://whitearmor.net/forum/index.php?showtopic=14806&view=findpost&p=179529
When printing these out, they should be 13/16" (@16mm) tall.
Modified version, front stripes fall forward
Paint options
http://whitearmor.net/forum/index.php?showtopic=8117