I 40 near Memphis tn overnight parking for motorhome

I would be concerned with safety in that area. If I was forced into an overnighter off of I40 that was free I would check for Cracker Barrels with bus parking. I would then give them a call and verify it's OK (and safe) to spend the night there. I've had good luck with that procedure and the managers will tell you upfront if you should keep going down the road to be safe.