Sounds like "Redbone's" tip is the way to go; no grinding, which is an alternative. Patience, a steady hand, and the correct tools will ease the job. You might want to try some-sort of sealer bead before bending the lip over to close things back-up.
For anything that you want to get some ideas-about, you can always peruse youtube to see what people have tried before. It doesn't have to be a VMax instrument.