I run the DD tail setup on my bird and the only problem I've had is the occasional tail-hard landing and broken props.

CN12 motor, EP-0320 (3020) prop. I have the tail prop flipped over to the other side of the bird (rotated 180 degrees) and flipped the plug around on the 3-in-1. The heatsink is seated to the motor with Arctic Silver brand thermal paste (the stuff you use on a computer CPU) and is secured in place with a very small bead of Arctic Silver brand thermal adhesive. In this orientation the tail prop draws air from the left side of the bird and pushes it, over the heatsink, towards the right side of the bird. Wiring is looped out & around, well away from the motor and secured with a small zip-tie. I used a Dremel to bore out the stock 'gearbox' so that the CN12 would fit snug and I drilled a small 3rd hole through the mounting plate in order to accommodate the 3rd screw hole in the motor (secure fittings... goooood). Popped the stock bearings out of the mount for the stock tail gear to save on the tiny bit of weight.

I have had 0 problems with this setup. 0 failed motors with quite a bit of flight time on the original. Granted I'm not a 3D pilot so I'm not throwing the bird all over the place. But I do move the CPP around quite a bit in the massive field behind my house. The tail is razor sharp throughout the entire battery pack. Rock solid in HH mode on the G90 and very nimble and precise in SR. I have tried this DD tail setup without the G90 and I really don't like it, feels almost too touchy. I highly recommend using a quality HH gyro with this mod.

All parts were ordered from AlleRC.com. All you need is the GWS CN12 motor, EP-0320 prop & the heatsink. (by pure chance 3 of the screws from a store bought baggie of replacement screws for the CX2 fit this motor perfectly, give it a little threadlock and you're golden)

Below are a couple pictures of my tail. (I know it may not be the prettiest but hey, what are we after here... performance or fluff?)