Rainedave,

I've used gallons of the stuff called "Liquid Masking Film" Greatest thing to ever come along for folks that Paint their finish on the aircraft. I think Dave Platt originally packaged it and sold it. I'm sure a good Engineering supply company may have the same "kind" of product.

Essentially, you Spray a lite coating of this or paint it on with a brush. Draw your design/Letters 'lightly' score it with a #11 exacto then peel up the piece you want to spray and "Voila~" Perfect edges, then when done simply peel the rest off, if you are using an "airbrush" then very little overspray.