IMO, a hi-lift with more than likely a larger than stock tire on the rear is too much weight for the rear door hinges. I can promise you if you add this when you close your door its going to be harder to close and you might have to lift up on the door to get it to close.
I have seen one or two people make a mount that goes into two of the roof rack mounting holes and that works really well and no need for a roof rack. Next best spot is on a front bumper, then inside using the rear seat bolts to attach it.