We do carry replacement filter inserts for specific branded air distribution boxes like the Replacement 14" x 7-1/2" Air Filter for Dometic Duo-Therm RV Air Conditioner # RA48QV, but they aren't HEPA rated. I do know that you can get rolls of HEPA filter material that you could then cut to fit the vent opening of your air distribution box, but we don't currently carry this. view full answer...