I also used a blade for the sides and had a sharp chisel that fit nicely in the bottom. I bought the replacement strips from NPD but I cut them to size to install in 3 pieces. 2 for the sides and then the bottom piece. Worked nicely for me. The replacements are very sticky, a one shot deal that's why I decided to do it in sections.
As above. I just did mine a couple of months ago. Most of the felt can be peeled out. What was left I removed with a small old chisel that fit right in the bottom. Just scrape as much out as you can. I used the replacement felts with the adhesive already on. Cut into three strips after measuring and installed the floor first and the sides second. Pretty easy.
Russ, would be a good idea too to grab a can or 2 of cavity wax. I spray it in crevices and the back side of panels that will be covered up. It is great to seal against moisture down the line. It will run a bit when 1st sprayed but sets up rather quickly and any that drips where you don't want it, easily wipes up. They usually come with a spray wand to for hard to reach spots like between the wheel house and quarter panel.