I have the Mini P180 as well and was debating for a long time about watercooling. I must've looked at this page 100 times. I finally did it though.

Sorry for digging up an old thread =x

Here is my build.
It can also be found here: http://www.overclock.net/water-cooli...mini-p180.html

Not much modding. Took out the top 5.25" bay and mounted the rad on top of the case.
I was able to put 2 standard Yate Loon 25mm along with the MCR220 up top after taking out the top 5.25" bay.

Specs:
Asus Rampage II Gene x58 mATX
i7 920
6GB G.Skill DDR3-1600
BFG GTX 260
3xWD 500GB AAKS Raid0