ICE Thinking about a "proper" install?

5. The other bits!

Don't forget to factor in cables, use the biggest cable you can for power and speakers. This will give less resistance, less voltage drop and more power! Also, use good quality RCA leads to send the signal from your HU to your amp(s).

Soundproofing. Dynamat type sound proofing will help stop panel vibration and thus increase your stereos volume. It's expensive, but it's a worthwhile investment. A layer or 2 in the boot and the same for the doors will be adequate for most installs.

Installation is also very important. There's a saying 10% equipment, 90% install. The sub enclosure needs to be well built, completely sealed (apart from where it doesn't need to be, e.g. ports) to get the most of it. Some prefabricated boxes really aren't up to the job, and they may not necessarily be of the correct volume for your sub. If you build your own, then you can decide on how thick you want to make the enclosure walls, bracing, shape etc. The speakers also need to be solidly mounted to cut down on unwanted resonance. This will give improved sound quality.
Make sure your amp/s are cooled sufficently. With a large percentage of amps DO NOT MOUNT THEM UPSIDE DOWN (e.g. on the underside of the parcel shelf). Amps produce heat, which it dissipates. Heat rises, so if it's upside down, the the heat would be radiated out, only for it to rise back into the amp, causing overheating and possibly destroying the amp. which is not good . Check your amps installation guide before fitting.