First, Good News... As reported on TDOT, "I-75 South Reopens to Traffic Following Rockslide in Campbell County" - See more at:
http://www.tn.gov/tdot/news/38148NB schedule still remains on or before March 24, but at least getting through there from the North doesn't entail a detour around the rock slide area anymore.
We went down to Blue Water Key RV Resort three years ago from Cincinnati. On the way down, we stayed at the KOA in Cartersville, GA. Reasonable price, nice owners, very convenient, but not right on I-75 South. A good stopping point.
2nd stop was at Paynes Prairie Preserve State Park just on the south side of Gainesville in a town called Micanopy. Beautiful park, nice sites, very convenient to I-75. Great stop over place as well.
Next stop was Outdoor Resorts of Chokoloskee in the 10,000 Islands area immediately west of the Everglades. Beautiful RV resort with great access to the Everglades. I highly recommend it. I'd take the opportunity to visit the Everglades as well if you can plan a day or two for it in your trip. Take the tram tour from the Shark Valley Visitor Center on the North side of the Everglades. It is a must see. Just make sure you take the 1st tour of the day. That is the time of day when all the wildlife is out.
Have fun. We loved Blue Water Key by the way.