On the other hand I am working and THINK I can break 20MPG at 75MPH in my custom 93 Full size van
https://www.facebook.com/media/set/?...4247153&type=3
With a custom built 383 which has a low/mid RPM Cam running a custom cam with Roads Lifters, and ceramic coated pistons and cylinder heads for lean burn running, custom OBD1 computer with special chip, and I will be adding extra EGR to both lean out the A/F ratios, try to burn left over fuel, and help over come pumping loses.
Lastly I plan on adding a second over drive (old Borg Warner unit devoiced from a 3 Speed w/OD) allowing my high torque engine to run at 1600RPMs at 75/80MPH.
As we rarely cook food on a road trip, a ice chest serves us well, and as our outing rarely last more than week max, shower, or other things are not needed. And as I plan on spending any over night stays at say KOA type camp grounds where I can get A/C will be able to run a small heat pump A/C unit for comfort.
Where as my even super MPG 2000 Mercury GM only got 24/26 MPG at 75/85MPH 20MPG at those speeds will be great considering the great ride, comfort and load carrying of this van.
Rich