[99LeCouch]

Find a 98-99 Buick LeSabre with the skinny tires and front bench seats. I get 34-35 mpg at 60-65 mph, it's comfy as heck, and it's big/stereotyped enough that folks don't give a second thought to passing me. Plus you can sleep in the back seat if you're short enough, and it will hold gigantic volumes of stuff. I've done numerous 12-14 hour car trips in it, and have arrived without soreness or stiffness.

Aerodynamics can be improved by making an upper grille block, weatherstripping the hood to the headlights and bumper, smooth wheel covers, and putting fairings in front of the front wheels where they jut into the airstream. The rest of the car is a blob with okay aero.