My 2 cents.
Can i just say that enclosing the wheels will have a dramatic effect on aerodynamics, and make your goal easily achievable. You should look into the Human Powered Vehicle speed records for bicycles. Those are supremely aerodynamic vehicles capable of 80mph using less than half a horsepower! The basic outer shell design could be easily adapted to the scale of your vehicle to allow the same roominess, while still maintaining nearly the same drag coefficient as an HPV. Which is i think below 0.1cd.
On the HPV land speed record vehicles, i've read that nearly half the aerodynamic drag comes from the tiny slits where the wheels are exposed, as it does from the rest of the vehicle body. And these slits are for really skinny bike tires capable of only turning the front wheel an inch to either side. This goes to show how much aero drag an open wheeled vehicle can have in proportion to the aerodynamic body it's attached to.
Your goal is easily achievable, it just depends how much you want to sacrifice to styling.
