I cut the top out of my p180 to put in a triple radiator and included the rear fan vent in the design. One thing you could do that would make it easy on you would be to use the existing fan vent and just cut the hole for the second one- that way there's be lots of room for tubing and fittings, less cutting, and no need to worry about not overlapping the top fan. However, I do think that there would be enough room to mount it in front of the fan but working inside the drive bays with bolts and/or fittings and tubing (depending on how you do it) is a pain, but doable as you can see in my build log (i'm assuming that the layout of the top of the p182 is the same as the p180)
http://www.hardwarecanucks.com/forum...rcooling+antec