Northern Lites like even pressure material on the undersides because the basement sides are carrying most of the load. You want a more firm even base that won't tend to imprint the heavier sides.
I found cutting the plywood into three strips easier to handle. Each are one foot wide by 8 foot long. In your case you could stack up the strips in the truck for the extra cab clearance you need and still be able to handle each piece easily.
My strips have the rubber matt glued to the plywood strips. It's very important to support all sides of the camper which are carrying more weight. Esp. the rear overhang area. So in order to do this properly I place additional smaller strips behind the wheel wells to carry the widened profile of the camper.