Just to clarify the difference between Tobin's recommendation and mine:
Tobin (I believe) has you taping over the whole grill, which saves you the
trouble of taking the grill off, and depending on the color of plastic
bags used, may give you a new color element for the front of your van.
My approach is to take off the grill (requires half-turns of five screws)
entirely, revealing a fresh-air intake duct MUCH smaller than the grill
area.  This intake duct is all you need to tape over.  If you use black
duct tape, no one will see any difference between your van's summer and
winter plumage.  While the grill is off, wash the bugs off it, scotch-
brite it, and paint it all black.  The faux chrome paint around the edge
was just grey flecks by now.  Start planning how you are going to replace
the missing cardboard-soaked-in-asphalt panels between now and next 
spring.  Get a colorful car badge with a national flag or family coat of 
arms and mount it over the VW in the center of the grill.  Remount grill.
(half turns of five screws).

B.