Ideally, if you can take the time, try to have at least 2 or 3 days minimum, ideally longer downtown between 200+ mile driving days, so you don't find it all gets too much. For convenience we enjoyed camping at the Kentucky Horse Park, and at night watching the fire flies, it was an unreal experience for us, wondering at first what all these lights were flickering around, lovely display they did for us uneducated at the time peeps. Kentucky is one of our favourite states we will return to again one day but for longer and slower.
Also if you are going to be in Texas and of course depending how long a trip you have planned, what about Big Bend NP? Also the Caverns of Sonora (Roadslesstraveled did a beautiful report on that).