In the spring of 2005, I did a test on the passenger and drivers door with the sound deading material (like B-quiet), but I used cheap Lowes home store "Leak Stopper" roof mending tape. From what I can tell, its the same stuff.
The drivers door in the video does not have any sound deading material (stock), the passenger side looks much like how MightyArt (this link) did his.
The results were amazing. The passenger door sounds as solid as my Dad's 2000 Audi A4 doors, not like a tin can (stock Vanagon). The video really does not do it justice. I wish my camera could have better sound!
This was cheap ($12) and easy to do. When it comes up an upgrade, this is a no-brainer!
Video (Window Media Format 700k)
Update! June - 2005 After seeing a later model Vanagon, it seems in 88/89 they added this type of material to the doors. If you have an 88 or newer Vanagon I'm not sure it will sound much better than the later ones do stock....