Anyone who's still looking to do this mod, I came up with a different way of attaching it. I though it would be cool to make it removable so I could take it off for cleaning and polishing.
I got a tube of steel epoxy and some 1/2" neodymium hobby magnets. I mixed up the epoxy putty and rolled it into a long, thin tube and formed it into the underside of the chrome ring. Once it was all even, I pressed 2 magnets into each side of the ring into the putty.
Not only do the magnets stick magnetically to the steel putty, but then the putty dried to the magnets. And these magnets are f'n STRONG!
Now I just gently attach the ring to my tank, and put the gas cap back on. No other mods were necessary. The only thing I did was lay a sheet of 120 sandpaper on the tank and rubbed the chrome ring back and fourth to slightly conform the bottom of it to the shape of the tank.