Or just get a steel boat. Thats enough insurance for me.
Having stayed long term, and short term, and every term in between at various yards and marinas - I have not once been asked to provide proof of insurance. Maybe I've been just lucky though.
In my opinion at least - there are many better things that money could be spent on. Like a heavy anchor, lots of chain, good line, good chafe guards, and actually going cruising and getting experience that will help prevent trouble. My 2 cents at least....
Then again, we also haul out during hurricane season.