Personally, I wouldn't put speakers in the rear deck.
Not super high end equipment (lots of power) but then the listening environment isn't great (wind noise being the culpruit) either. Awesome in the garage or loafing in city traffic but futile on the highway at anything but full tilt volume - you can't drown out noise with power - it just gets noisier. On the highway I use a pair of very good sound isolating in-ear buds.
Some things to consider (my opinions only so ....). The holes in the rear deck are just that - holes - and all of the noise in the trunk has unimpeded access to the passenger compartment. The speakers are not a barrier to that area at all. Secondly, given the noisy sound environment, anyone sitting in the rear will experience sound levels in the pain threshold range in order for the driver to get much benefit. Lastly, speakers closer to your ears (the front) are way more effective and enjoyable (why headphones are so cost effective) then ones in the rear that are further away and behind your ears.