4Ryan6's post is very helpful however he's ice box/rad is outside his case. I personally don't want a big icebox like that. I'd prefer it in my case. Since I'll have a small amount of distillates water running through my system I won't need 1 gallon of ice I'll need a few ice packs. I'm only running 1 loop to CPU.
The volume is what enables a larger degree of control over the temps, I'd think it is feasible to have a smaller version but inside the case would be more difficult to swap ice in/out and potentially more risky for your hardware,
maybe a small custom res/tank is a plan you can investigate but I'd definitely have it external,
but as I said before Ryans the man on this, he will have experimented with various options before arriving at his current set up
and don't forget to insulate all your tubing