I'm easing my way to a Kamm back, currently MAX has Bonneville spoilers top and bottom. And 115 mpg at a steady 45mph.
45mph was the minimum for the X Prize roundy-round race, and it's also the usual freeway speed lower limit, so I took it as my success-or-failure benchmark speed. At 55, I'm just barely under 100 mpg and at 50 mph I'm slightly over 100 mpg.
I'm confident I could break 100 mpg at 55 if I'd...
--do my mileage tests without unnecessary weight on board (no luggage and less fuel would knock off a hundred pounds)
--close in the back and sides of the stern
--add spats to the rear fenders
--cover the front wheels with pizza pans (I lack the fender overhang I'd need for Basjoos-style front spats)
--put a fairing on the headrest/rollbar
--put a tonneau over the passenger's seat
--do my testing in warm calm weather
--put the mirrors inside the windscreens
...and probably any three of the above would tip the scales.
But I'm probably going to pursue weatherproofing before I get into much more ecomodding. It doesn't matter how good the mileage is if I don't drive it, and non-roadster season is rapidly approaching. Besides, once mileage is sniffing at triple digits, the rewards from improvements diminish. The difference between 95 mpg and 100 mpg is a gallon every couple thousand miles.