I avoid Atlanta at all costs. If I wanted to do mostly interstate driving, I would try taking I-10 across FL to US231 and up to Montgomery, AL. Then I65 north. Once at Nashville you can take I-24 over to I-57 in IL to I-74 over to Bloomington, IL. Or at Nashville, continue on I-65 to Indianapolis and pick up I-74 to I-39 in Bloominton, IL and then straight shot up to Madison and points north. I39 comes into IL at Rockford so if you want to go to the Chicago area you will need to head back east. If you are going to the Milwaukee area then stay on I65 at Indy and go up to Chicago.
There are some nice COE campgrounds just south and east of Nashville as well as a couple of COE's in S. IL around the Rend Lake area. If you are going to the western part of WI, try the river road from the Quad City area up and along the Mississippi River and take advantage of the COE campgrounds on that route.
If you aren't in a hurry, look at the COE campgrounds. I've found them all nice and they are all on water of some sort.
If you do go up I57 in IL you can jump over to St. Louis on I64 and visit there.
If you go up through Nashville and stay on I-65 you will go through Bowling Green, KY, and can stop and see the Corvette Museum and just north of there is Mammoth Cave. You can head west on I-64 at Louisville and go to St. Louis or pick up I-57 and go north in Illinois at Mt. Vernon, IL.
Almost too many ways to go but my experience in the "mountains" of the southeast are to stay on the interstates unless you know the local roads or have a great deal of time.
