It does not look like your motorhome will fit in any of the accessible sites in Lake Griffin State Park. This area is tough to find good sites. There is a park Fisherman's Cove at Lake Harris which is on the southern side of the lake. We were not impressed when we drove through it but it would do in a pinch for us.
A really nice park, Grand Oaks RV and Resort, usually has availability unless they are hosting an event (horse shows and dog trials) is about 20 min (12 miles or so) north off of Hwy 441 in Lady Lake. We found it when we were looking for a place to attend a nearby dog agility trail. 50 AMP, FHU,paved roads and sites, small but excellent restaurant onsite, great hosts with selection of pull thru and back in sites although only a few sites have shade. Beautiful property with great views of the pastures from the campground. Price point runs about $50 a night.
If I recall Southern Palms is okay it has been awhile. However, if I remember correctly the sites are grass unless there are some accessible sites that we missed. Not familiar with Holiday RV park.