Like many of us I was overwhelmed with the task of replacing that Fugly Green cloudy mess of a plastic window after 16 years. As a SoCal car it's rarely up but when it is its horrid. I finally gave in and thought I'd share what worked for me in case someone else may want to take on this task in the future. The good news is you can do it in a day or less once the materials are obtained. This is if you have a partner be it girlfriend,wife, whomever. This job is better done with a person above and below. The tools used were a stitch awl from EBay, thread, Basting tape, and many little pins/clutches.
Firstly, remove old stitching, plastic window, and use your old crappy window as a template to trace onto new plastic. There is a backing on the inside of window that holds the stitching and you will reuse that. Add a 2 inch margin around the plastic then cut. It makes it easier for pushing the awl through as you have extra material to hold onto. Now glue the backing onto the inside of new window with fabric glue and let dry. The plastic I purchased was a Regalite 40 mil DOT for automotive use in clear. Next, you will apply basting tape to the outside perimeter of the new window just outside the window opening where you traced. With partner hold up new window to canvas and now pin/clutch the plastic. You may have to move and re pin several times to even out the canvas so as not to end up with many gather points. Try to keep softtop extended fully during this time.
Now decide who wants to be on top! Missionary position actually works best. One person pushes the awl in through the existing holes as partner below uses either his fingers or tool to hold the canvas taut as she's thrusting down. All the person does below is keep threading through the loop created by the awl. Once you get the hang of it, rythem, it just took about 6 hours total. You will be quite surprised how fast it can go. My biggest fear about this entire project was that it might gather so much in many places and end up with creases once extended but to our amazement it didn't. Those pins/clutches really did the trick. It's really not that daunting a task but allow a good day.