There is a casino (the Miccosukee Resort & Gaming) at the intersection of US41 and Krome Avenue (997) north of Homestead about 8-10 miles. We've stayed at Miami Everglades RV Resort just off Krome Ave. I'm not sure about the possibility of parking at the casino, but I know that most casinos generally let campers park in the lot while they "visit" the place. I also believe others have posted on this site about staying the night there prior to heading down to the keys. Plus there's usually parking lot security at casinos if that's a concern.
PS: Didn't see the previous post about the casino above prior to posting.