You say there is some coupling and then you say you will fix that by intentionally bonding it. Isn't that 100% coupled?
At that point you have to make the arbitrary decision of which current carrying conductor you want to bond. Until you bond one, they are all the same and none of them has a particular affinity to the frame of the generator.
As I said before, small Hondas are not bonded and I have not heard of any problems with them.
