Another vote for Topsail Hill - we have stayed several times before and I have just made reservations for a couple of weeks next Feb. I dont know if you could stay 4 months though as it is a state park - even if you could, it would be costly.
The Royal Coachmen in Nokomis - as others have said - is very nice, although we haven't been back for quite a few years. I think that these days it would be even more expensive than Topsail Hill, $70 a night wouldn't surprise me.
We have also booked some time for this season around St Augustine, and also couple of weeks at Land Yacht Harbor Airstream park at Melbourne.
Rates are very reasonable at Land Yacht harbor, and you likely will have no problem getting a spot if interested in going across to the Atlantic side. The park is very well maintained, but no pets allowed - and I'm not even sure about kids! There is no pool either, but nevertheless it is a good home base and we are usually away someplace all day anyway! Nice beaches nearby and just over an hour or so to Orlando.
PS - at one time, not so long ago, we used to go to Florida without reservations and never had a problem, in more recent years we have found it very difficult to find a spot and for that reason, this year we have made reservations for our entire planned trip including stops at Savannah & Charleston on the way home.
You can waste a lot of frustrating time trying to find a campsite in the winter months of you don't have reservations - we learned that the hard way!
Brian & Connie Mitchell
2005 Classic 30'
Hensley Arrow / Centramatics
2008 GMC Sierra SLT 2500HD,4x4,Crew Cab, Diesel, Leer cap.