I can tell you that the biggest risk to a tape in transit is getting lost, not getting erased.
The tapes we get from the different vaults are virtually all shipped the same way. A heavy double walled cardboard box, inside are all the tapes in a single poly bag and peanuts to protect the tape from angry baggage handlers.
DO NOT!!! mark the box as "fragile", "Magnet Material enclosed" or anything else. This will ensure the box gets lost or damaged.
In the states, all the tapes come UPS ground. All. To be honest, I don't remember how the last European tape was shipped, but it is usually either Fedex or DHL.
All the best,
-mark