i've done these basic images up in sketchup. although it shows the hdd in an enclosure, the actual enclosure for the hdd would be removed as its really not needed. mounting holes in the bottom for the hdd of course, probably just "hot glue gun" the usb hub in place.
3 DC jacks on the rear, one for the raspbery pi, one for the usb hub and an optional one for the external hdd. This means you can either use a 3.5 mains powered or a 2.5 usb powered.
i havent worked out a stable and easy way to move the RPI's power draw from somewhere inside the unit without making it the size of a large ITX case yet. keep hearing people say "dont power the PI on a powered hub" so i wont lol.
the round hole in the front is for a power switch, the rectangle is for a front mounted usb port and the small square hole is for the remote control receiver.
oh larger slot in the rear, mandatory "exiting cable" slot because moving ethernet and hdmi ports to the rear is a pain and i honestly cant be bothered. also acts as venting for the hdd lol


anyway, if you see somewhere for improvement, post up and let me know.