Eric,
I've towed a 6x8 trailer that's boxed in (fully loaded with junk). I'm not sure of the weight either but it did the job well. The mountain pass will be slow going - the power mode will be your friend there - just pick a speed that the VX can maintain even if it's slow & don't keep shifting up & down just to keep the speed up. See if you can find a trailer with surge brakes - that'll help on the back side of the mountain pass.
The only other thing I'd mention is to keep both hands on the wheel. Side winds can be quite entertaining if you're not prepared.