A 1/32 or 1/64 inch crack lets in water and leads to rust and paint failure.
I've got a seam where a professional body shop used polyester filler and
rust bubbles are starting.  The whole rig flexes all the time.  Modern cars
have fewer and shorter seams with more spot welds and lead is used to seal
them, which also fuses tightly and flexes a tiny amount due to its
malleability.  It will crack though if the joint isn't strong.

Stuart

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Liberte, Joel
Sent: Wednesday, November 21, 2012 12:29 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: seam sealer

That would also suggest not welding the seams together if they are flexing,
but do they really have to and how much do they really flex/expand/contract?
That would also effect the seam sealer choice if it's considerably, which I
highly doubt would be the case.

Joel

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Stuart MacMillan
Sent: Wednesday, November 21, 2012 12:07 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: seam sealer

Yes, automotive seam sealer sticks better and flexes more so it doesn't
detach or crack. Those panels do flex, and the seam opens and closes
slightly. And, it's sandable and paintable.

Stuart