The "Zap" is an excellent compariable.
I think the following can also be lumped in there with Doug Miller's design. If we can find the Cd's of these cars, maybe we can make an educated guess about Doug's Cd.
Razor...........lots of turbulence coming off those front wheels.
Razor at stoneleigh...
I know this has four wheels, and is open on the sides and top, but mass wise it's in the same ballpark, and lot of drag coming off those wheel flares.
Kit Cars [group] most recent on FlickeFlu
Drag off the front wheels seems to be a part of most traditional 3-wheel trikes.
EDIT: According to this the Edision-2 had a coefficient of drag of 0.16
X Prize Winners Look Weird ... With Good Reason | Autopia | Wired.com
I read elsewhere, that the Zap World car made the top five finalist. So how bad could their aerodynamics possibly be? An exposed rear wheel, and drag inducing front wheel farings not too dissimilar to Doug's,
I'd say he might be better off than we first thought.