I did this a couple weeks ago and thought I'd show the set up.
Basically I didn't like the fact that you couldn't add a 120mm/140mm fan at the traditional exhaust spot.
My CPU cooler is set to intake so I really wanted to exhaust that air as soon as it passes thru the rad.
The two 140mm fans on the left door really seem pointless.
So I decided to see if I could fit some kind of fan in the big hole at the back of the case.
After measuring the hole I discovered it could be a nice fit for some 80mm fans.
So I picked up two 80mm Noctua NF-R8-REDUX fans and cut a groove in them and to my amazement they were a snug fit and looked quite nice in grey.
Noticed 2-3C drop in temps using the temp probe so happy with the results.
No modification to case is required, just don't cut thru the fan shroud!
 

That's pretty sweet. Going to try this myself when I get a chance. Since I have a 86 I need to eventually order more fans for my setup.

miniml
That's pretty sweet. Going to try this myself when I get a chance. Since I have a 86 I need to eventually order more fans for my setup.

Glad someone liked it!
It actually worked a little bit better that I expected it to.

80mm fans are effective as well only if they are not loud, if you reduce sound. 
 
Is it possible to fit Noiseblocker Blacksilent pro 92mm 1300RPM or they made and 80mm 1500RPM.


 
DG-87 is great, maybe these fans could fit better in DG-86, but everything could be resolved with little work.
120mm are not necessary.