A guy we ride with uses a 4runner to haul a car to the track, it's a Z3. With a trailer it has got to be a pretty good load. He really likes the way it behaves.
I Don't mean to poop poop your ideas, BUT. Rule of thumb for long haul of a trailer with a vehicle I have always heard half of rated..... Anything above that and the vehicle is working HARD! OK for a weekend camping trip, but I wouldn't take it through the Rockies.
I don't have any suggestions that you would like, sorry.