Steve two way to lessen the bump steer is one insure that the tie rod is parallel to the ground when at ride height and two use the longest tie rod possible. That is why I chose to use a crossover system where my tie rod goes from the driver side to the passenger side this makes for a tie rod that is a good twice as long as if it were to run along the frame.
If you are going to mount the box ahead of the axle put it as far forward as you can get it, if you can put it right behind the bumper. Another problem I ran into may not be of concern to you is when I tried mounting the box as you are thinking witch works great on the pickups but with the 10.00 22.5 tires on my 6100 the tire would hit the box and severely limit my right turns. If I were you I would try to mount it temporarily and then turn the steering from lock too lock and make sure everything clears.
