Overpacking Exceped Package Radioactive Material is certainly permitted. When you make a sealed overpack where you cannot see or access the Excepted Packages inside, the rules on markings and labellings of the overpack are the same. For the limits on radiation and activity, consider the case of ordinary dangerous goods overpack. Each individual packages inside the overpack is limited to the maximum kilograms or litres as specified. You are not adding them to make an overpack. It is the same with Radioactive Material. You do not add the radiation or the activity of each individual Excepted Package inside the overpack. There are limits on Transport Index specifying limits on PAX, CAO or charter aircrafts but the Transport Index for Excepted Packages are ZERO.