Most hard drives are fine running passive.
Depending on the lineup a rear exhaust can provide a little airflow over them.
It is possible to mod a front fan into one. Lian Li EX34 is ideal, mod it and then use it for the intake. Linky Ma Link
I can't get you temps of my hard drives, to old and no temperature monitoring in the case, but they have ran 24/7 for 3 years just fine.
Depending on the lineup a rear exhaust can provide a little airflow over them.
It is possible to mod a front fan into one. Lian Li EX34 is ideal, mod it and then use it for the intake. Linky Ma Link
I can't get you temps of my hard drives, to old and no temperature monitoring in the case, but they have ran 24/7 for 3 years just fine.