First off, Homestead is probably not the best town to 'boon-dock' ... lots of crime in that town.
Everglades has some great camping, and it's not that far off the route heading to Keys. You might drop into the park, the first CG is fairly near the entrance, and is worth the effort. If you do that, don't miss Royal Palm, a short nature walk about four or five miles from the campground and the entrance.
Park is about twenty-thirty minutes or so from the highway... worth an extra day to see Royal Palm too.