Which interstates will you be coming into Atlanta and then which one leaving? I'd guess I75 coming in? Leaving likely would be I75 or I85 depending on where in FL you are headed (Gulf or Atlantic side). Your route through Atlanta would really depend on that.
We've done Walmart and Flying J's for quick overnight stops (stopping after 9pm and heading out before 8am). Do a Google search for walmart overnight or walmart RV. You'll find LOTS of info.
If you travel I75 south of Atlanta, there is a nice GA state park called High Falls less that 1 mile off exit 198. I've seen lots of folks do 1 night stops there. There are a few pull through sites so you could stop without unhooking boat.