We stayed at Hide-A-Way RV in Ruskin last winter. Cost was about $600 per month plus electric. It is a 55+ park. They have a nice pool and lots of activities. Horseshoes, shuffleboard, aerobics, water aerobics, kayaking, bowling, golf, dances, pot-luck dinners, entertainment, bingo, etc.
It is located on the Little Manatee River south of Tampa on Route 41. Easy access to Tampa and/or across they Skyway Bridge to St. Petersburg or south to Bradenton and Sarasota for dining and entertainment. It's also a quick trip into Sun City for meds (Walgreens, CVS, Walmart) and shopping (Publix, Winn-Dixie, Walmart).
There are a lot of really nice full time residents there and many of the "transients" come back every year. It has a nice "neighborhood" feel for an RV park.