Only leave 1/8" on the lip. Don't wory about the welds.Mine have been done for 4 months and no problems. I did not cut enough the first time and had to do it again. Used a good quality body shop glue to seal and touch up paint. Its strong and un-noticable.
Hey fletch, I started about at the line in the middle of top part of wheel well on the front and went to the plastic clip at the bumper. Just tapered the cut.The key to no worries is the top quality glue. A little more than 6" to be safe.