(f) Doors. A vehicle specified under this subchapter shall be equipped with doors of a type used as original equipment. The doors shall open and close securely unless the vehicle has been manufactured or modified to the extent that there is no roof or side. Tailgates, except on vehicles where the tailgate gives access to the passenger compartment, may be replaced with wood planking, nets or other material that will prevent loss of load. Tailgates may be removed when optional equipment, for example a truck camper, is added.
I think that means that they aren't gonna like tube-doors either.