Point mallard in decatur is a nice park, they take reservations this time of the year, just not in a few months of the summer, but it would be about 7-8 miles off the interstate i believe.
The park in athens - Northgate RV Travel Park http://www.alabamarvtravel.com/
is a good place if you are stoping for the night. It is very convenient. less than a mile off the interstate.