The same guy on you tube that shows how to cut the front fenders also has a video on how pie cut the repo step fit the rear fender .
https://www.youtube.com/watch?v=2q7XNfT9I-0
I have also been told to heavily undercoat the repo fenders before driving if you have show paint. A rock thrown from the tire will star ding the paint from the inside. The undercoating (thicker the better) will help dampen some of the shock.