need to stiffen the rear end on 03 altima

[dacarver2005]

03 3.5se altima 20x8.5 wheels just added with 245 35 tires rubbing in the back cut and rolled the fenders helped a bit but still rubs on certain dips or if i have weight in the rear the front is fine factory struts in the rear kybs were added in the front a yr ago before the wheels were installed do i need to put kybs in the rear will they stiffen the rear and stop the rubbin or do i need to go the way of springs