do kicks and components need boxes?

I've seen numerous pics of peoples kicks and component speakers, but what I'm wondering is do they need boxes to be fabricated or can they be placed into factory holes. In the case of the kicks, can you just glass an enclosure without a back, or does it need to be "boxed" in? how would one enclose these things with the correct size box if the car itself won't allow anything that is t he proper size for the speaker?

Best sound quality for a set of speakers in your kicks will come from an air tight enclosure. For your component speakers, you can use factory provisions for the tweeters, but your best sound stage will come from having the tweeter mounted within 6"-8" of the woofer, so it is advisable to mount the tweets outside of the factory provisions if at all possible.