Port Huron to Clarksville IN is 421 miles and you should be able to do it in 8 hours. Clarksville has 2 RV parks. Addmorervpark and Louisville KOA. My personal opinion is that the KOA is way overpriced but with Addmore you must have cash or a check. They do not take credit cards. Addmore is about 1 mile from the expressway while the KOA is right up against it therefore more noise.
Clarksville IN to Atlanta GA is 423 miles but you are limited in RV parks immediately north of Atlanta. On the bypass South there are a couple between Atlanta and Macon.