I've done some amateur act airbrushing with templates & I'm struggling to understand why you would want something thick like coroplast for the spray template itself? Typically masks want to be thin to preserve the sharpest edge possible. Think typical masking or striping tape. Thickish templates have another downside & that's the vertical wall holds wet paint, so if it has sufficient buildup, can back flow down & smear muck up your work. Are we talking the template or the sign material? The stencils I've seen are like 1mm thick mylar (or one of those tough plastics that are solvent proof). Thin templates can also wrap around curved surfaces a bit if that's a parameter.
