I know that Black Wow is good for black plastic trim , but what about the grey and charcoal colored trim . I need something to put on the step plates of running boards that is not slick or greasy .
3-4 coats will last more than a month on its own. A quick refresher coat after every other wash or every 2 weeks, it'll last a very long time. It's just the initial application that'll take more than one coat. If the trim is really bad it'll get absorbed into the plastic very fast and it won't look that great. If that were to happen, don't worry and keep adding coats until you are satisfied.