I agree with what Nathan and LaLeLu said. The issue with mandatory insurance has nothing to do with what your boat is worth. It's all about being liable for potential damages caused by you, or your vessel.
Having insurance is only one of many expenses affecting the costs of living onboard in a marina. If you can't afford that nominal expense, I believe you will be in for quite a shock by the total cost of living.
True Blue . . .
sold the Nauticat