I think this thread is a better place for this topic than in my 'window fixin party' thread since it was mentioned here.

Two of the doors we worked on had no vapor barrier (VB). Those got the trash bag/duct tape treatment.

One of the doors we worked on had the VB still in place but it was completely covered with moisture.

If you have any doubts about the effectiveness of that VB or the importance of it, it works & it's needed.

While replacing speakers on Wifey's car last fall, the driver's door VB was torn & the OEM speaker was completely covered in mold.

It'll only take you 10 minutes to replace the VB if you already have the door panel removed. Do it.