Yea that is a kewl design for no attic Luke.
Here is what my a/c in the garage basically looks like. Click the pic if it is to small to be viewed.
note on the top view...I added some panels on the front sides & the very top of the box to seal the a/c unit in.
note on the front view is that my box sits in the hole that I made in the ceiling. It actually is screwed to 2 x 4"ish lumber that anchors it so I dont bump it or what ever.
There is no back view because I dont find it required. The back is a solid piece of plywood and can be seen in the top view. The bottom view well I am just lazy if someone does not understand I will make a pic for it.