I keep the OD off and keep my speeds at 55-60 mph. I only got about 9.5 MPG though but thats to be expected.
I took my 2002 LX470 to the Outer Banks, NC last week without towing a trailer.
I got 15.4mpg, 15.9mpg, and 15.4mpg. Looks like towing is going to require 40% more fuel.