Roof And Pillar problems of the 2005 Jeep Wrangler

I was backing up at night on a steep curved driveway. My front wheels went over the curb. With the front wheels over the curb, I elected to go forward over the curve and down the grade. The body cleared the curb, and I slowly negotiated going forward over the curb. The rear wheels cleared, and when they did the car bounced. I heard the rear bumper hit the curb. The resulting bounce caused the bumper to come up and crimp the corner panels of the body, worse on the left than the right. The action also cracked the fiber glass roof on the right. None of the under car was damaged. There was no visible mark on the tail pipe either. Note that this was simply going over a curb in a vehicle listed as trail rated. The mechanic at the body shop speculates that either the bushing connecting the bumper to the frame is inadequate or the extended length of the Jeep unlimited makes to too flexible; it lacks a central support.