You probably would void your insurance as well, there was a boat moored up the river from us that had a bad fire, there was a genny stored onboard, but not in a BSS compliant way, even though it was empty of petrol therefore supposedly not a fire risk. They got no insurance pay out.
After that I was so paranoid I had my genny locker welded/fitted by a tradesman who is also a BSS inspector, I wanted to be sure. I don't run it onboard, only store it, as others have said, that can be expensive to do safely.