I second the jks approach. I use a door mirror from Walmart to cut my covering on and lay up "skins" of monokote multi-color schemes on the surface of the mirror. Get everything laid down and stuck together on the mirror, then transfer the whole piece to the plane and iron it down.

The Walmart mirror is not made of glass exactly; I'm not sure what it is, but it's thin, lightweight and semi-flexible, makes it very easy to handle around the shop. Inexpensive too.

Overlaps of at least 1/4" or jks' 3/8" will stand up well over open structure. Just make sure you have a bubble-free bond along the length of the overlap. It's a heck of a lot easier to get your stripes straight and constant width when you're working on a flat surface; then when you transfer to a curved surface, they look sharp. Use an aluminum yardstick and single edge razor blade to cut your covering on the mirror surface.