"mm" wrote in message
U-haul says for ttrailer rental:

Must be equipped with a hard top if it is an SUV or Jeep. U-Haul
does
not allow any type of sport-utility vehicle not equipped with a hard
top to tow U-Haul equipment.

How come?

SUV's are of "unibody" construction. This means the entire body of the
vehicle is the structural support for the vehicle - whereas trucks and
older vehicles have a steel I beam structural frame under the vehicle.
I don't know about a jeep?

Anyway so far as stopping and a LOT of weight from a trailer pushing
one the rear of a unibody vehicle, I would imagine that a metal top
would provide additional support. Without a metal top, then I suppose
the vehicle might want to fold in the middle like there was a hinge in
the middle and the rear end would fold up. (With a severe stop.)