I used these HEPA filters available on Amazon: https://www.amazon.com/dp/B0B25QQG93
I tested the air filters before using them in the enclosure to see if the activated carbon was acid-washed. After running air through the filters in an enclosed space for over 24 hours I saw no signs of rust on various steel and iron objects. I believe that the activated carbon is not acid-washed.
I used an old Delta 92mm computer fan. But, any 92mm fan should work. Make sure you get a fan with good static pressure to improve airflow through the filters.
The author marked this model as their own original creation.