A rig that size won't fit on a U-Haul dolly. The tires will be too wide to fit on the ramps. Also, if you tell U-Haul what you're planning to tow, they won't rent it to you.
You might rig a conventional tow bar to the front of the frame and flat-tow the truck. (remove the bumper and bracket right to the end of the frame rails). Use heavy-wall square tubing, and reinforce all the welds with gusset plates. Be sure and remove the driveshaft to prevent transmission damage on a tow that long.
Jerry
