O.K. I'll ask, what are you doing with 6 TONS of books!
If you are truely looking at carring that much plus a trailer w/ van and misc inside, then you definetly will want to go with a twin screw. Don't even think about that as a option. You must remember many of the toll roads will stop you from proceeding if you are over 21,000 lbs on a single axle.
Not sure how long you plan on staying out (fulltime, couple weeks, a few days) but if longer than a few day, don't even look at a garage coach, full motorhome is the way to go here. You could easily put the kind of weight your talking in a tri axe stacker with room to spare. And like Sean said we are talking semi-trucks here, these trucks are used to hauling 60,000 lbs.
Keep us posted as you work out all the kinks in the plan.
Bill
2003 28' Show Hauler Motorhome on a 1995 FLD 120
www.showhauler.com