I've already been known to camp in my car before, so hotel/campground reservations aren't an issue for me. It's a PT Cruiser, so the size of the back is like a steel & glass tent if I take out the back seats, and I even have a home-made cloth thing I can hang to cover the windows all around like a curtain. But it would be a long drive in an old car that I'm trying to minimize mileage on, so I might switch to a trip to Kansas City where I can stay at a relative's home and ride with them or drive a rental car for the much shorter distance from KC to the center of the path.
A bigger issue for me than what part of the country to be in or where to sleep while traveling is what exact spot to be in at the exact time. The ideal place for me would be where there's a good natural landscape view instead of a city/town full of buildings, but I expect the famous view spots in the national & state park4s to be packed at that time so I can't count on getting in or out, especially in places where the eclipse path passes close to a major city like KC. In my own car, without being tied to any particular place & time along the way, I figure my best bet might be to just be parked or pulled over at any place I find along the highway that looks like it could be good enough and easy to get in & out of, so I might favor taking my own car on the longer drive just so I can improvize at the last minute.