A wise man once told me "if you have to ask, you can't afford it." My advice would be to pay cash for the boat, typically, boat loans are not the greatest ideas. The boats depreciate much faster than cars/trucks. As far as insurance, mine is around $150 a year with tournament coverage. A storage space for a 20 ft boat is going to be costly, around $100-$200 monthly for that size.
if you can't afford to pay cash and don't have a place to store it you may want to reconsider...... just sayin