Staples is selling a 36"x36" cardboard square that is supposed to fit a 11'. Good price too....... But to be serious, I think this might work? Looks awful though.
FORD 2011 250 350 SUPER DUTY WINTER FRONT & BUG SCREEN - eBay (item 400177348912 end time Dec-30-10 06:36:23 PST)