Try the Corps of Engineers Parks along the Cumberland River. We stayed at the Cordell Hull COE and each site was on water, as fingers of land were poked into the river, either naturally or built that way, I'm not sure now. But it was beautiful. These are not long term parks, I think 14 day limits, but TN has so many of them, that you could probably make a hobby out of going from one to the other for the 14 days limits. If you qualify for a Golden Age Passport, your stay is half price.
We stayed at another one on Percy Priest Lake south to Nashville that we liked also, and a couple of others that I've forgotten about now. We no longer travel through that part of the country, but TN has some of the prettiest public CGs we've seen and I would have liked to spend more time in them. The sites are normally huge, with lots of space between neighbors, each site with a "right of way" to the water and large enough for any size RV. Most have no sewers, because of the proximity to the water, but do have a dump station usually conveniently located. Also they do have water and electric, but a few are just boon docking.
If you're looking for a commercial cg for long term use, I can't help you there, since we haven't used any that I can recommend for that. (meaning, I don't know if they have long term agreements.)
Daisy