Measure the distance difference between the mounting points on the roll bar.
Measure the distance difference between mounting surfaces for the roll bar in your cargo area. Subtract an inch and start cutting/trimming there, as it is easier to trim off more, not so easy to add more, just don't forget to add in the thickness of the mounting plates, carpet, padding etc if there is going to be anything between the roll bar mounting plates and the cargo sheet metal.
You will probably want to angle the front mounting plates as the tops of the fenders wells slope inwards, at least on a 3rd gen they do.
