Parenting Physics Object to Player

I am working on this backpack sort of thing and when the player uses this entity the bag is placed onto the player’s back. I wanted to make the bag an actual entity because different things will happen when the bag on the player takes damage(like when the bag is shot while on the player’s back) however I am having a lot of trouble parenting it to the player at such a spot on his back that it doesn’t impair his movement.

I’m using this bone on the player when I’m setting the bag’s position and all that.
“ValveBiped.Bip01_Spine”

Anyone?