If you get in there just sanding/grinding the paint off the frame around the bolt hole and adding some silicone to prevent future corrosion should do the trick. Another good idea is to run a heavy wire or ground strap from G1 to G2.
To be as effective as possible, you need to run a tap in the holes and get every drop of used Loctite out. Don't reinstall Loctite when you put the new hardware in....add a star washer instead.
I have installed car audio and competed in car audio competitions for years. I'd be a little cautious on adding any additional ground straps as there is a chance you can induce noise into the audio system. Its easy to do.