I have visited the local Fedex Ground Hub and they handle the packages as if it is a demolition derby in these buildings.
Long boxes are handled the worst of all, this side up labels completely ignored. It is amazing that more models are not destroyed.
The night I was there there was a FAI F3C pattern plane in a large wooden case and it was was being handled properly!
If you are shipping in cardboard it MUST be double boxed to survive period.