Actually not. I hate to rain on the OP's parade and don't know if the OP has been to the Keys before but I can think of a ton of other places that are better to ride than the Keys.

I have never ridden there myself but have driven it several times. It is a beautiful ride, there is no dispute there but but traffic moves very fast. I do not think it would be much fun to have traffic buzzing in your ear over all of that distance not to mention the fear of some driver dozing off or getting distracted by the scenery.

As far as couch surfing, I would doubt you are going to find much along the Keys. You usually fair better in more populated places. Members are more pentiful and more active. Add the fact that the Keys gets more than it's share of transients I'm sure that makes a lot of members gun shy along this route.

I usually look at the percentage of response. If it is low, I usually don't bother sending a message.

Also it could be your approach. CS members are very much about meeting others. They are not involved to become a hotel room for travelers. If you give them an idea that you are just looking for a place to sleep, you may not get a response.