If you wnated to do a quick and painless experiment in front door
gasketing, this is how I would go about it without removing the front
door's.
Go to Ace Hardware , Home Depot, Lowe's, any household repair
supplier,and purchase a roll of foam rubber window gasket material.
It comes in various thicknesses, and width's.
It has adhesive on one side of it.
It is a comon item anywhere.
Cut the appropriate length for the front of the door, open the door,
stick the gasket on either the jamb or the door, and close the door.
A simple job, maybe a 5 minute job at best.
This would tell you right away how much that factory gasket is or isn't
going to quiet the interior of the Vanagon down.
It won't.
The front and rear wheel well area, and under the seats must be covered
in sound absorbing material.
The underside of the Van's wheel wells must be covered in heavy coats of
undercoating.
The front vent intake must be sealed .
I would start in these area's, and you'll find that this was the right
place to start with the noise prevention.
I don't have a DB meter..
I can talk to my passeneger without screaming to the opposite side of
the Van, and I can hear the radio without having it at full volume.