I have my 2 AirPod Pro "2" in Spigen cases. I don't have them in these cases for protection, but for hanging. They have carabiners that allow you to securely hang them from a pack, pocket, or button loop. The Nano Pop has this plus: it has a secure latch to hold the case closed. I have never had a problem with the magnetic latches on the present cases staying closed, but a physical latch would be nice. Right now it is on pre-order.
Here is a trick for keeping the covers on the Apple Charging case. Use a small amount Duco Cement where the existing adhesive strips are located. Duco is a standard cement used in the industry to hold and assemble plastics. I figured the only reason to remove the charging case is if the battery fails, you can purchase new charging cases from Apple.
