You can go either way, people on these forums go back and forth about what's better, in or out, but they're about equal, best way to tell is to test both ways yourself. You'll have in mounted on the inside of your case where the rear case fan is, just make sure the fans are both the same and both pointing the same direction, mounting them on the radiator is pretty self explanatory, just screw em into the screw holes. You're basically choosing between blowing colder air from outside of the case onto the radiator, but into the case (and it's warm air when it comes through), or blowing warm-ish air from within the case through the radiator to the outside, which is better for your case temperature, but maybe not ideal for the radiator itself.