It does need circulation... the heat will end up killing the drive... and that willnot be pretty...
but even in a computer if not properly vented (number of fans really doesn't apply) the drive will become hot....
I had to use masking tape to cover 80% of the extra holes in the front of my PC case to direct air over my PC's 2 drives... this worked great..
Something like this might be in order for the PS2 HDD... although I haven't even looked too much into it at the moment.
Urbigbro did a great job with his setup... Although you might not want to mod the case.
Even an older 40mm fan from a 486 or Pentium chip would pull enough air... I'd through it in under the side of the machine where the CDVD drive is... that overhang... then completely isolate the HDD bay with tape to direct the airflow...
also with more airflow you look at more dust and dirt... so the machine will most likely need cleaned more often.
PS3 Slim 320GB
PS2 v11 exploit w/300GB Maxtor
PS2 v10 exploit w/80GB Samsung - Network Games
PS2 v10 exploit w/60GB Samsung - Network Games
PSP 1001 3.52M33 w/10GB total storage
NDS DSReal 4GB