Unfortunately you're pretty far away to gamble that it will work out - that said, if it doesn't go smoothly in Key West, something will work out, you're not gonna be killed for trying and failing. You talked about buying a boat, so you have SOME money. I just rented an apt in Miami Beach, have only spent a couple days there. For as touristy as it is, you'd think that being a bum there is tough - but no, I saw dude passed-out splayed across the steps of an art museum right on the tourist strip of Ocean Drive, about 9pm. And in the daylight, about 2pm or so, I saw another dude just sleeping on the porch of a building (previously) under construction. I also saw undercover cops make a bust of a would-be thief, so it's not that cops aren't around, and I didn't wait with the sleeping bums to see how long they lasted before cops shooed or arrested them, but my point is that anywhere in FL is better than Philly, given the temps of the next few months ahead.
I suggest shooting for Key West, see how you can do, and if it's a hassle go to.. well, anywhere else. Another island as suggested, or on the peninsula somewhere. People sleep/car-camp on the beach in St. Pete, right by the bridge to Tampa, don't get hassled.
Key West properties are getting ridiculously pricey, so as Eden mentioned, there may be no tolerance for unsightly po' folk.