Lake Conasauga campground in the Cohutta Wilderness is a really nice campground. I've been there several times and its one of my favorite places to go when I leave florida for north georgia. U.S. hwy 411 runs south/north on the west side of the wilderness through Chatsworth and some smaller towns. I go into the forest from a small community called Eton just north of Chatsworth, but I know there are several other ways in. I'm pretty sure you can come in from Ellijay on the southeast side of the wilderness. Chatsworth is north of Atlanta and east of I-75.
I only recently became interested in jeeps. My wife and I are (were) backpackers and there are some great hiking trails in cohutta. We would set up a car camp at the lake conasauga campground and then day hike. I have been in my stock jeep and found a few easy and short jeep trails. There may be more, but I haven't explored for jeeps yet. I bet mountain bikes would be fun there. The forest road from civilization into the wilderness is a great jeep trail in itself. It climbs up into the middle of nowhere and the campground is so far from anywhere, that it isn't as crowded as most places. It probably takes most of an hour just to get from the town of Eton up to the campground. And if rough forest roads with the top down is pleasurable to you, then there are miles of scenic rides.
The campground itself is high in the wilderness and there's a dammed lake there. Many of the camp sites are right on the water. The campground is no reserve with the honor payment envelopes. Theres a nice bathroom/shower, water spigots, fire rings, etc. It's been a few years since I was last there. Again, it's a long way back to town for extra hamburger or camera batteries.