I'll offer a few suggestions.
For a more north location you might check out Rock Crusher Canyon in Crystal River. This area is called the Nature Coast where you can see and swim with the manatees. Crystal River is about 75 miles north of Tampa and 30+/- miles southwest of Ocala. We've stayed here and will be there for a couple of months next winter. It has a state park feel, but with FHUs and cable for a reasonable price.
http://rockcrusherrvpark.com/A bit northwest of Orlando you'll find Olde Mill Stream campground in Umatilla. This is a small rural town, but there is plenty of shopping and places to visit nearby. The park is very nice with nice sites and a good activity calendar if you're interested. We stopped here 2 winters ago for a 3-4 day stay as we moved around Florida checking out various campgrounds.
http://oldemillstreamrvresort.com/Further south, in the Port Charlotte/Punta Gorda area, although it's mail address in Arcadia, is Riverside RV Resort. It's really much closer to Port Charlotte and only about 5 miles east of I-75. We stayed here last winter for a week and really enjoyed our stay. Lots of activities, nice pool area, and a very large activity center for guests. It's a bit more expensive than the 2 above, but again, we wanted to visit a number of campgrounds to see where we might want to stay again for a longer period.
http://www.riversidervresort.com/Another park we stayed at and enjoyed very much, but this is quite a bit further south. Miami Everglades RV Park. It's actually closer to Homestead than Miami and is located in a rural farming area away from the big city. Nice facilities.
http://www.miamicamp.com/We went down a couple of years ago for 6 weeks and last winter for about 9 weeks. Next winter will be closer to 3 months and we reserved for 2 months at Rock Crusher because we like the setting, better traffic conditions, golf courses, great seafood, etc. We've stayed at state parks and private parks visiting various areas of the state. While it may be more expensive the further south you go you might consider the center areas of the state like Sebring, Winter Haven, Clermont, etc. (check out U.S. 27 areas) as prices are generally less as you move away from the coasts, but the parks can be just as nice. Good luck with your search.
