Any plastic box that accepts a lock works. Some have used kids lunch boxes, I used a MTM ammo box and a friend just used a plastic ammo can from Cabela's.
On my trip over I just put some TSA locks on the ammo box just in case they wanted to look inside, but the TSA locks are just for US airports. Just make sure that there is a handle on the box if you are flying inside of SA and need to place the ammo box with the rifle case. For the rifle case use padlocks where only you have the combo or key.