Why not just use the box your motherboard came in?
In the quest to cut down on shipping waste Taiwan’s Asus has a novel idea: What if the shipping container became the PC case?
That’s the idea behind a box the company will begin using from June to ship one of its Mini ATX motherboards. It holds the motherboard snug for shipping and is constructed so additional components required to make a PC can be added.
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Asus said the box is intended to allow PC enthusiasts to get their new computers up and running quickly while they search for the perfect case.
If you dig through the Ghetto Mod thread on [H}ardForum, using boxes as a permanent case isn’t that uncommon.