If the roofrack is the "factory" unit from a golf/jetta 3 (Trek/K2), I can
tell you that it won't fit a Vanagon. The crossbar and the roof clamps are
one unit as far as I can see. Therefore, not only will the rack not be wide
enough, but it clamps to the wrong shape of roof (you lift up the edge of
the rubber strips Ben was talking about and place the clamp under them but
hooking them onto the roof).

Sean B.
'90 V'gon, "Happy Bus", soon to be pseudo Wolfy
Torrance, CA
http://vgonman.vwtrek.com