Carefree of Colorado has brackets just for
Vanagons and Eurovans.  I think the Eurovan
version bolts on; the Vanagon doesn't--I
have them.  They clamp to the rain gutter.

Go to
http://www.carefreeofcolorado.com/

The pick Folding Camper, then Patio Awnings,
then SideWinder II.  You'll find the
brackets there for $65.  They might sell
them direct; I once got a part that way.

You can (barely) see the brackets in:
http://jones.colorado.edu/jones/syncro/camping1.jpg
I have since moved the awning a little and
used the third bracket--three came in the kit.

                Richard A Jones
                Boulder, Colorado