Here is our 19" 4U rackable rig prototype


We have 3x R9 290 and 2x R9 280X but it looks like they don't like to work together.
Testing with only the 290s, the ventilation was quite good and temperature was the same than in our open rigs (~90°).
We'll rewire with 5x R9 290 (the 1600W should be at its limit) and test how it goes.
We could also put the PSU near motherboard, and space the GPU a little bit more.
If it works then we'll be able to fit 10 rigs per 19" bay, and make a nice looking laser cut front panel for each case

Eric
All i see there are extra costs. The enclosures, the super expensive USB risers and the computer fans (while big ass box fans are like 25 bucks).
I highly prefer my way. Buy metal frame shelf, modify it and fit 10 rigs in it. All this for practically nothing.