hmm, what i did is, as i have no holes on side of my acsing, i have kept one bracket of front panel , where u insert CD/DVD opened,
and now it makes a very optimal flow of air (i tested it with my ciggerete smoke movements)
what ever u do, keep 2 things in mind,
balance the air flow, means air in = air out (keeping in mind hthat you have 1 PSU with big fan taht is drawing air out)
else, what it'll do it create a semi vacuum inside casing, and air will be forced into casing, resulting dirt getting into ur system via CD/DVD drives.
I have recently lost my brand new CD-RW just because of this, as I have a 120MM fan at back (massive throughput of air), and now as I have ole bracket open, even I install 2 fans, wont matter, and never even found any dirt on my CD/DVD inner sides.
I want performance out of my syste, not beauty. that is why i bought simplest (but good quality casing)