The power supply mounts with the back facing forwards, and uses a power cord extension to reach around to the rear of the case. The case is double-layered here, the mounting holes for the four screws can be accessed through small openings in the outer front layer. As you can see however, there is no opening in the front for the exhaust; this is where the fan and duct on the bottom come into play. For those power supplies with a built-in on/off switch, this mounting location makes accessing it very inconvenient. Conversely, the screwless 5¼" drive rails make installing an optical drive literally a snap.
The bottom panel must be removed to access the external 3½" drive bay or install a fan into the power supply exhaust duct, something I highly recommend doing. The Duet does not come with one but most users will have a standard 80mm case fan lying around. Note that when I first installed the fan I put it in backwards, after taking the picture I realized my mistake and pulled it back out and turned it around so that it blows air out of the case. I opted to forgo the floppy drive and installed a second hard drive in that bay instead.
I installed an extra 120mm exhaust fan next to the CPU socket, leaving the opposite side open. This should help evacuate hot air from around the CPU and when used as a mini-tower it functions as a large blowhole. Strangely enough, case temperatures were 2° C worse with the Duet stood on end than they were lying flat. I verified that in both cases there was enough of a gap along the bottom for proper airflow. Without that gap (created by applying the included stick-on rubber feet) a substantial amount of airflow was blocked and temps quickly rose above safe levels.
