If the P180 has a standard 120mm fan, that is where you can put the radiator, inside the PC attached to case, with fan attached to radiator.
If no 120mm fans, you can attach it to the door inside, and drill a series of vents (holes), or onto top panel blowing upwards.
BTW, I think that the TT-BWse is the best WC choice for a hundred bucks.
The antec P180 is not the best case for a water cooling system :!:
befor you jump on the defensive, let me explain.
Every watercooler enthusiasts worst nightmare is a leak, and it DOES happen even with the best of setups and precautions. the good thing is that many times the water trickles down the tubing and the most critical components are spared (not always anyway )
With the P180 the chances of that safe trickle is reduced and guess what ? the component that MUST NEVER come in contact with water is placed at the bottom of the case right down a potential trickl/spash path.
Guessed what it is??........yeah the PSU :!: once in contact with water POW :idea: PUFF-POW and raw AC current direct from the mains. i need not describe further the damage that can occur not only to your PC but you in person.
Antec in an attempt to get better noise reduction levels made this design and it just dont go with water cooling.
Piece of advice- when building /assembling a water system, try to locate the radiator and pump outside the case for two obvious reasons ,(this i succeded to do with my own setup using another Antec)
1, radiator outside gives better temps
2, both components out side minimises danger of soaking your components if one of them springs a leak.
(only allow the parts that are indispensible and must be inside the case namely tubing and heatexchangers/spreaders.
If you look at the connectors on the TT BigWaterSE, you will see that they have a 5mm hose over a custom brass 6mm fitting, then a threaded pressure lock nut to further sinch it down on every fitting. Very quality designed system that is virtually leakproof. and only $100 complete with fluid!
I design mine inside for quietness, and the heat difference from internal to external is not more than a degree or two celsius.
In overall aesthetics, it is worth it.
Intel Prescott's do not throttle till 80C, and no way would even the TT BigWaterSE even running internal let that CPU get up that high, unless you do not plug in the pump and fan.
Come on, I realize that you get a tad better cooling external, and slightly better odds of leaking not causing problems, but if you are somewhat careful, it is not hard to make system leak-proof and internal work just fine, and it is a much cleaner looking system with less chance for movement of hoses and wiring, which in itself can lead to reduced accidents.