Print in PETG or ASA. Put two 6x3mm neodym magnet in each hole. Put a little drop og glue on the back of the outer magnet and hold it to the AUX fan casing, when this sticks, remove the cover and glue the inner magnets in the bottom of each hole. Your HEPA filter is now able sit on the outside of the Aux fan casing , with no need to dissemble or to glue magnets inside.
HEPA filters that fit this model are model -GL2103 HEPA - google them on Amazon , ebay or Aliexpress to but. Note: YOU have to remove the plastic cover ofthe HEPA filters to fit it in this printed part.
Magnets are 6x3 mm neodym magnets