Some good points mentioned above, particularly zoning and maintenance issues.
Could be a nice gig and the numbers certainly seem to work out.
My Dad and step Mom lived aboard their boat (57' w/ 3 bedrooms) and they only lasted 6 months before they got sick of life abroad and having no home base. Of course you'll have a home base.
Only negative I see would be hurricanes but it's not a hell of a lot different than surrounding homes.
Hell, go for it and see if it suits you.
Scott