To gain access to the interior, simply remove the two side panels by unscrewing the thumb screws holding them in place. There is a metal shroud which Montech has thoughtfully tooled to offer four cutouts for cable routing, while also offering screw mounting holes for two 120 mm fans. The only downside here is the fact that the cable routing openings do not come with grommets here or at the top edge, as they are only present on the two cutouts to the right of the motherboard. In the rear, things look pretty traditional with a very large opening for easy access to any CPU cooler brackets you may install.
You will find two dedicated 2.5" mounting plates for SSDs below that opening, each held in place by a silver thumbscrew. To the left there are actually two more dedicated placement options with black rubber rings. You will also find three pre-installed Velcro strips with some basic cable routing already done out-of-the-box.
At the front, below the shroud, there is the metal hard drive cage which can hold two 3.5" drives or a mix of one 2.5" and one 3.5" unit. Above that the room is intended purely for cooling with two 140 mm intake fans clearly visible in front of the case body, giving you lots of room within for long GPUs. This area of the Air 903 base also allows for a third 140 mm fan to be installed. I can see users moving the identical one from the rear to the front, so that they could go out and buy any black 140 mm fan for the rear instead while keeping the look in the front clean and consistent. On the metal plate towards the front of the case you can clearly see the mounting holes for the SSDs as well as those for E-ATX boards.
In the rear, the PSU bay comes with two black foam strips on which your PSU will rest. Above that, the seven expansion slot covers are secured with individual thumb screws. At the very top, you will find that third fan set to exhaust air out the back, which may be adjusted in height to line up with your CPU cooler.
Looking at the ceiling, the full length of the Air 903 Base is utilized for cooling, with the mounting offset as much as possible to allow for the remaining space to be used for cable routing.