Surface Pro external cooler

Summer comes! The air is hot and my surface pro 3 too. If the cpu heated up, the frequency of my i5 cpu will drop from 2.6GHz to 1.85GHz or even lower! That absolutely slows down my computer. I want to find a external cooler, but there are few, expensive or I just don't like.
So I decided to 3d print my own one!

All you need is:
- two 40mm 5V DC fan (Sleeve Bearing fans are good enough, cheaper and more silent comparing to Ball Bearing fans)
- a usb power meter
- four or eight M3 screws