Does it have to be metal? I'd like to see wood stencils for repainting cabs. It seems like a lot of the fuss and bother of repainting cabs centers around stencil peel, and the lack of the proper overspray (which no one seems to want to replicate, because you really can't with a stick on stencil).
The factory used stencils made out of brass AFAIK and just held it up to the cab and sprayed away. I made a prototype a long time ago for the front of a countdown cab out of 1/4" plywood and just sprayed right through it, worked great, correct amount of overspray. Only problem is that I used semi-gloss so it didn't match the sides of the cab. (I'd prefer to use flat/matte paints when doing a cab anyway, and if you wanted the gloss, apply a clearcoat afterwards. I like original look, though.)