Whatever you do, do not cut slits. All you're going to do is make a mess .Trust me, I've done a quite a few fender rolls and have seen it all. As long as the rear end is bolted in with axles,Eastwood roller will fold that lip,no matter how strong you think it is.I've had to push out quarters almost 1.5 inches with a roller to clear the tires on some cars
Here are couple pics of a hack job I had to deal with
And here is a pic after all that mess was cleaned up