I posted recently that with a Quick n Easy roof rack with 2X4 cross bars
on my tin top Vanagon, I noticed a significant reduction in gas mileage.
Between   jobs, I popped off the rack and my fuel consumption returned to
it's normal level of ~23mpg.   Then,  I found some more work and put the
rack back on, for two tankfuls...again dropped to just below 21mpg.  Then,
two more tankfulls,  but  with the rack again sitting in my shop, not on
the van's roof...back to 23 mpg, +/-.

  Some will say "so what?  What's a few miles per gallon difference
anyhow?"   Well, I was just budgeting for my annual "trip to the dentist"
this winter....to the desert Southwest near Yuma, Az.   It's about 3000
miles round trip from near Portland, Oregon.  I will be able to go 460
miles further at the 'no rack' fuel consumption rate.  Roughly $100 bucks
in savings on gas costs.  That will pay for  a tooth-filling (+) at the
dentist there in Algodones, BC, or a couple of sets of eyeglasses..The way
things are right now for us 99ers, every expense that can be avoided is
important...so a few mile per gallon better gas mileage does make a
difference.  The Quick n Easy  racks do go on quickly and easily with the
flip of cam-type levers...
  Don Hanson