Do you have a Tractor Suppy Company near you?
They use alot of foam packingin shipping.Most of the foam blocks are 16"x16"x16".They give you as many as you want and arrows come out of them easily.They also hold up verywell.
The guy who use to work on my bow at the pro shop turned me on to them.He was a great guy.It's to bad he moved to Delaware.