Step 1) Pick up some foam tubing. You can find some at your local Hardware store B&Q or some other shop. Take special note of the diameter of the foam tubing to ensure the tube fits.
Here's what it looks like out of the package.
Step 2) Peel back the corners of your rubber door stripping on the frame of the car. Mine for some reason were all cut already. Does it come like this or is this just wear and tear? All four of my corners were already torn.
Step 3) Insert foam into the tunnels of the rubber door stripping. Spray with Aerospace 303 to lubricate the foam and rubber tunnel and slide approximately 18"-20" into the rubber tunnel. I personally ran the foam tubing about 15-18 inches along the top of the door and a good 6-8 inches along the side. It's important that you use some type of lubricant (not that kind... ) to get the foam tube to slide smoothly into the rubber tunnel. I sprayed very generous amounts of Aerospace 303 and it went in nicely.
Step 4) Step back and admire your work. The foam tube should sit flush like this and when you let the rubber flap go, it will cover up the tube and look stock.
Step 5) Repeat for all doors. And maybe the trunk?