I've done a little over 20K miles in the past three years, virtually all with a toad, and the bulk of it on Interstate or US highways. Traveling, I'm moving just at 35K Lbs, and I cruise at 1700 RPM, (which gives me 63-65 or so). I deduct generator fuel before calculating. I've averaged 7.4 mpg for the entire time.
John & Diane, fulltiming since '12
'02 DS 40, FL, 3126, '04 Element
John & Diane, Fulltimers. RVM103 NHSO
On the road since June '12 with Lincoln, the guard cat.
2002 Dutch Star 40, Freightliner, Cat 3126, 2004 Element