When I painted my Series 5 many years ago, I tried the recommended spray polytone over tacky primer on hard surfaces. two problems I encountered were the procedure is a pain in the butt , because you are shooting two different paints in close succession and you either need two paints rigs or better be quick and cleaning your gun for the next coat. second , like Eddie says I found the polytone not durable on hard surfaces and I figured it would never stand the test of time. My solution was to head to the local auto paint store and they did a great job of matching my Polytone colors with their enamel (Dupont Centari was the product I used) and this is what I used on my cowl., doors ,gear etc. I can't tell the difference in color between the two paints and after 16 years , I know I did the right thing because it has held up well. I did have to flatten the sheen on the enamel a bit to match the polytone but that was easy with the flattener mixed into the enamel. Bruce N199CL