Get yourself so me fine line tape and place it around the outside openings of the louvers. next take some 3M light adhesive masking tape and place that over the fine line tape, after that use blue poly coated paper to mask the rest off and you are good to go. Expect a small amount of overspray which you can remove with a base/clear (less harsh and abrasive) rubbing compound (#3 at most)......


Bill S.