We have off-roaded our 560 "almost SUV" a number of times. Our almost is not quite SUV height but higher than the standard height. We have done a number of roads in Death Valley, East Mojave, Joshua Tree and other places. I am not familiar with the White Rim Trail, but my quick look at some pictures on line, I would say it is quite feasible with a 550 SUV. I would suggest rock flaps on the tow, we beat up the front of our trailer a bit our first time off road from kicked up gravel, even with the Alcan cover. Also, be specially careful everything is well stowed in the trailer, it will get shaken around.
One place to pay special attention is in the main cabin be sure nothing can move around and hit the inside door locks; if something hits the door lock you can be locked out, the key won't open it. If both sides get locked, the only way in is through a window at least damaging the screen. Don't lock the windows so at least you can slide the window if this happens.