Remember to consider your fans power draw when calculating headroom on the PSU. I think 120mm fans run around .33a on avg - so maybe about 4w each? If youre really pushing the limits of the PSU, your best bet is probably an open air rig w/ good spacing, and an external cooling solution if possible. Heres my setup for example - the 8x64 rig is on the left. The spacing alone is generally enough to keep these reasonably cool (40-45c) even at 70-80f/21-27c ambient. The cabinet is more for noise suppression and dust control (this is my garage/workshop too!) but the airflow helps on those summer days when temps get up significantly higher. Many people just point a box fan at their rigs. (btw, the fans on the one rig arent necessary, but I didnt bother removing them as I had the power headroom):
There are different solutions for each case. For example in my garage im using 2 pipes - one for remove hot air and one as inflow. Also, i often see rigs in boxes with 120mm fans both side.
So your solution is nice but for your conditions.