AWESOME video Mark!
Aside from the suggestions already made, I would put something on there about the square footage, age, price and condition. Also you need contact info should someone have any other questions and want to see it.
In the State of Florida, an agent can't list and sell a property unless the seller owns the land underneath it, so that rules out timeshare, houseboats, and manufactured homes or trailers where the do lot rent and don't actually own the dirt underneath - which means this will be up to you to do (or you can use the help of a real estate consultant for marketing - get with me on this for more info).
I agree that I'd show more pics of the lifestyle... get some fishing shots, sunset and/or sunrise shots, what you want to do is place the viewer in the lyfestyle they are buying into.
Contact everybody in your area that has anything to do with water, and put flyers with your slideshow on them....scuba companies, charter tours, fishing, any marina's, see if you have a communtiy website for Marathon you can post on, or something related to the Keys.
You may want to put a sign on your boathouse saying it's for sale (in the window, or if they will let you post it on the dock ?) Does the place you rent the dock from have a bulletin board you can post a flyer on? In the keys, most advertising is local... My brother just came from there on a fishing trip, My husband works for the Sheriffs office in the marine patrol dept, so I get lots of waterffront inquiries from all these water enthusiasts... since my husband has worked with boats all of his life, has his captains lic, is a certified scuba teacher, Diver, yada yada yada, his dream (and many others like him) is to move to the keys when they retire and open up a dive shop/charter co, etc. So don't rule out marketing to specific niche markets like this.
Good luck and if you have any questions about the consulting method, email me at email@example.com or call me and I'll be happy to give you some idea's on that.
Now for my final question..... WHY would you want to move from there and where are you going?