With 30x9.5R15 tires, nothing should rub, even beyond max payload.
You'll hit the rubber bump stops before your rear tires hit the fender wells.
I've had right at 1300# in the back of my truck (marble tile & granite), and the bump stops made friends with the rear axle, but the tires never rubbed anything.
Load that truck up! Most Rangers have over 1000# payload ratings, so have at it.