I think if I double up the tailgate cables (2 on each side) and run the unit on 2"x6"'s in the bed of the truck I'd feel a bit more secure. The boards would reduce the load on the tailgate (the front of the unit would act as support) and leave only a small cantilevered load on the reinforced tailgate supports. Its all overkill, but if it keeps you from losing your mind while travelling then its worth it.
I have seen some less than stout tailgates (FORD base model F-150's, not bashing) but I think my GM is sturdy enough to handle the reduced load.