I do this process.
I use a Snap On Crud Thug to remove all the seam sealer and gain access to the inner seam.
All you have to do is get all the rust converted or removed and it will stay away.
ALL means ALL, both inner and outer parts of the seam.
The inner part is very difficult to gain access to in certain locations.

POR Patch has heald up well on seams that were very rusted.
I use 3m sealant when the van is a 8.5 out of 10 or better.

Very deatailed writeups on the samba for this, including pics.

dylan

________________________________
From: Matthew Thyer <matt_thyer@HOTMAIL.COM>
To: vanagon@GERRY.VANAGON.COM
Sent: Thu, February 25, 2010 12:11:29 PM
Subject: POR 15 in the seems

So I've been working diligently to clear paint from the floor in Zeno in preparation for the arrival and application of POR 15 treatment.� Who knew that a wire brush and a grinder could be so much fun?� Anyway my question concerns similar treatment to the exterior of the van.� I'm thinking seriously of grinding out the seams the little bit of rust that may currently reside there and then treating these problem areas with POR 15.� 

Questions.� Has anyone else done this before?� What should I be concerned about?� Are there gotcha's you can point out before I discover them the hard way?

Thanks,

-- 
Matt Thyer
http://zenoswagen.wordpress.com/� � � � � � � � � � � � � � � � � � � � �