Mounted on plywood.
The frame (GPU suspension) is made from old
STABIL Metal Building Kit parts I inherited from my dad and borrowed from my 8yo son.

A fourth GPU is forthcoming, as are two big-ass case fans that I will somehow mount on this so they blow inbetweeen the cards.
I will add a third dummyplug and put that thing into a friends basement for free electricity, remote-controlled with logmein.
the cards are 6950 (1GB unflasheable) running at 840core / 800mem for 1050mHash/s altogether.

Like the materials you used -- very functional while being inexpensive.