Tony, your Vanagon (unless it has been modified somehow) should be fuel
injected.  The reason that earlier vehicles have carb icing problems is that
they had a carburator.  It has a venturi inside which, because of the
evaporation of the fuel, can become very cold (like when you put alcohol on
your skin and it gets cold) and ice up.  Your fuel injection eliminates this
problem by injecting the fuel after the throttle plate, directly before the
intake valves.  So the problem you are having could be that your fuel filter
has water in it and it is icing up during cold spells, or you have water in
your gas, or perhaps some other explanation, but not carb ice.
Take a good look under the hood and look for any loose, disconnected, or
frayed wires, vacuum hoses, etc.  If all looks good then go check out the
fuel filter (have something to plug up the hose from the tank with unless you
want a gas bath <refreshing!>).
Have fun.
Ken Wilford
Van-Again
John 3:16