We stayed at Knight's Key for just 4 nights about 3 years ago. It has a pretty laid back atmosphere and some of the sites were somewhat generous with space. The sites nearest the marina were pretty tight though. While they don't have sewer service they provided a pump out service and the fellow handling this seemed to be pretty active.
We enjoy a good long morning walk and Knight's Key is just across the highway from the old bridge that runs parallel with the main highway. The old bridge is a great place to walk or bike.