If it has brakes I think probably not much of a problem.

I don't know though how stable it would be on the highway. any push from a side wind instead of acting on the hitch will act on the roof, causing roll of the car unless it has perfect aero balance.

I think I'd rather have a hitch down at or below the center of gravity.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.