I cut my fenders similar to yours. I had a problem with them flopping in the wind and actually lost one while pulling my Jeep with my RV. I installed a screw on the top of the fender (going into the fender support) and haven't had an issue since. I also installed a marker light. I'll try to take a pic and post it here later.
You can fill it with weld, grind smooth and paint. This method takes a lot of time but will good.