wudnt freezing the sub cause the metal to contract which can cause the coil to burst? well there is a rumour that a cooler interior will give you a rise in SPL level. the inside shudnt be too cool though, but jus cool enough. keep in mind this will put an additional load on ur electrical system unless u have upgraded alternators an batteries. an tint your car heavily to maximise your A/C. and dont have your car in the heat before testing as if it is too hot ur amps may trip when its time to test.