Definitely best to patch with metal, but POR Patch is another alternative.
Here is an old write up I used years ago:
http://www.highperformancepontiac.com/tech/0306pon_windshield_channel_repair
/

The A pillar is a one piece welded structural member and you don't want to
mess with it.

Stuart

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Jim Felder
Sent: Monday, January 27, 2014 11:03 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Need a-pillar metal replacement

For a friend. See the picture at

<http://www.knology.net/~felder/Vanagons/pillarrust.html>

Only needs the outside skin. Let me know.

Thanks,

Jim