I had the same problem with my filters. I just added a piece of canopy foam to both sides of the filter to seal up the air gap and now it fits tight.
I'm not too impressed with Napa either. I went through O'Reilly's and ordered stuff online. It was at my door in 3 days. A little cheaper than Napa too. If you have over $75, it free shipping. Napa in the town I live really has a problem with Mopar, especially poly parts. They can't seem to get it right. Oh well, thank God for ordering stuff online.
Keith