I made a "casing" for my rig...just a Plexiglas sheet, with the ATX holes pattern cut by a laser. Screwed in some mobo stand-offs, double-side taped the PSU and voila! Couldn't not be simpler.
In addition to the main sheet, there are three little parts (if you look closely at the screenshot w/ the mobo), this is used to install a third video on top of two others (not shown...I don't have riser cable yet). The reason for this is to avoid air flow problems with all 3 cards side-by-side.
PM me if you want the design file (cannot post attachment here). If you have access to the proper machines (e.g.: laser cutter or CNC) you can make your own in no time. Ponoko.com is another option (upload design file and they cut it for you). Also, I can make some in exchange for BTC...again, just PM me. Plexiglas sheet comes in 4'x8' so I need at least 10 orders to get things going and not loose money.