Well, I did this a few weeks ago and replaced it with some 0.085" thick GE UV-treated Lexan that I cut from a 3' x 4' sheet.
You need to remove the seats and rear interior panels. Contrary to the manual, you do not need to remove the rear hatch, just prop it up, unbolt the lower bracket on the hatch struts and swing and tape them out of the way. Disconnect all the wires and then cut through the window sealant with a long razor from the inside of the car. It takes a lot of patience and is a PITA. Don't cut near the aluminum or the glass, try to cut in the middle to avoid damaging them. You can clean up everything later. Eventually you'll be able to remove the glass. Mine weighed just over 9lbs with wires and trim and the lexan weighed 2lbs.
Wearing gloves is a good idea. Also, I sprayed a little WD40 into the sealant score marks made with the razor to try and soften the sealant and let the razor glide through. I don't know if this really helped or not. Just be sure you don't get any on your hands where they can slip and get cut with the razor.
Went for a quick drive without the divider window and it was loud. Even worse was the engine heat blowing into the cabin when the side windows were down.
Make a window template to fit. Lexan expands/contracts so leave some room. I cut the Lexan with my handheld reciprocating saw using the finest blade I could find and a slow speed. Take your time cutting and protect your Lexan so it doesn't get scratched. It should come with a film that you remove after cutting. Sand the edges (I actually polished mine) and test fit. I used ten bolts to secure it to the frame, with rubber washers and slightly oversized holes in the Lexan to allow for expansion/contraction. I put 3M sealant strips (the little sealant 1ft. long "strings") around the outside perimeter to seal. This cuts down on the noise, but with the firewall insulation removed it's pretty loud in the car now :wink:
Dave