if you havent bought a head unit yet...get a Nak 6 in-dash CD or even top line Eclipse 6 in-dash CD. Its funny how i got so tired of constantly opening the trunk...and you will too.
but if you already have a HU and your getting a changer ...mount it behind the pass seat(not underneath) Most changers have adjustments to mount it at 45 degree angle with adjustments. and the pass seat is most logical because it allows you to reach back there to pull out the magazine easily