Pickensville is nice, but a little out of your way, I think.
Not sure of your exact route, but try Lake Lowndes SP in Mississippi. Nice and probably on your way if you're coming in Hwy 78. It's just over the AL/MS line on the MS side.
Also, if you want to keep coming toward Tuscaloosa (past Pickensville), try Lurleen State Park. It's right on the way if you're on Hwy 78. Call 1-800-ALA-PARK for reservations and info. It's not as nice as Pickensville, but for a one night stop-over it should be fine.
If all else fails, come on in to Tuscaloosa and go to Deer Lick CG (another COE park). It's pretty nice but a little out of your way (approx 8 miles off of Hwy 78).