GA 53 from Calhoun, GA at 75 east can be done to Gainesville. There are a few hilly and very curvey areas- especially east of Jasper and before Dawsonville, but with appropriate lower speeds you'll be OK. The route leans towards the scenic side.
I now avoid Atlanta roads like the plague.285 is so rough, jammed with traffic and loaded with construction. I do not find it RV friendly.
Another nice alternative is to camp at the Corps of Engineers parks on West Point lake at LaGrange instead of Lanier. Very nice campsites available- and a bit milder weather usually. And the benefit is you totally avoid Atlanta with 4 lane all the way to FL from Calhoun.
For that option you can take 4 lane GA 53 west off 75 at Calhoun down to US 27 in Rome then 4 lane down to LaGrange. Then its 4 lane down to Columbus on Interstate 185, then the GA 520 at Ft Benning down to Tifton and 75 again.
We use that route running north south all the time. At worst its taken us 15 minutes longer than the 285 circus.