Primers are not created equal by any means.
There are many too choose from and it really depends upon what filler products and paint products you plan to use with them that makes the most difference.
Most of all they are designed to be top coated and will help the adhesion of the right product.
Once all the layers are in place, you will have a secure system to keep the elements out.
Rust however works from within and shows up on the outside surfaces last.
Prep is the key.
You can transform rust, encapsulate rust, or neutralize rust.
With that said, you will not permenantly stop rust.

dylan�

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From: Florian Speier <groups.florian@GMAIL.COM>
To: vanagon@GERRY.VANAGON.COM
Sent: Wed, October 14, 2009 5:32:50 PM
Subject: is primer/sealer weathertight?

A few weeks ago I did my seams and surrounding three inches, at the typical
rust spot where the camper stuff is welded in on the drivers side. I ran out
of time after applying primer/sealer and thought thats ok to wait a while at
this stage.......
now we had two days of solid rain, and I have micro bubbles under the primer
about an inch away from the seam, and worse, something slightly rustcolored
at a few seam spots.
Obviously I have to redo a few things, but I was wondering whether my
assumption that primer sealer is weathertight was wrong, or if I did the
whole thing wrong......

thanks
florian