I didn't see a good write up on how to do this, so I took some pictures as I did it today. My car is a 2003 SSEI with the Monsoon sound system as a reference.
The first step is to remove the bottom of the seat, there are two clips on the front of the seat, pull up on it and it should come off. I didn't take any pictures of this, but this is where your battery is. If your not comfortable with this, then you probably shouldn't continue.
First remove the two bolts holding on the seat belt buckles. Mine were 18mm and rusted in place, I had to use penetrating oil and a breakover bar to get them loose.
Next you have to unclip the top of the seat back. There are four clips along the top that have to be released. I took a long flat tip screwdriver and hit the end of it with my hand. It'* harder to find them than to get them to unclip. If you get into the trunk and look up, you can find them.
Now the seat should come out, here is a pic of the back so you can see the clips.
Here are some pics of the seat removed.
Now to remove the rear deck.
You have to route the seat belt out of the rear deck and remove the C pillar trim panels. Pull the top of the panel loose then pull it up to get it off the clips. There are two push pins that have to be removed also.
The rear deck should now come out, but if yours is like mine the insulation is stuck together and it won't budge. I was able to get a hand under it and slowly pry the foam insulation apart. It ripped in a couple of places, but after that it came right out.
Don't forget to take the center seat belt off the rear deck.
Here'* a pic of the bottom of the rear deck, if you look close you can see some of the ripped foam.
Installation is reverse of the removal. Putting the C pillar trim back in was a little tricky, I pulled the top push pin and preinstalled it in the trim. I was able to leave the bottom on in place.
Hope this helps.