Adding another SMD to a citizen problem

Well i tried putting a backpack on a citizen’s back.

Now how the hell do i get it to work? Ignore the texture problem, i just couldnt be assed changing the VMTs. Thanks in advance.

EDIT: Damn you FP censoring websites >_> anyways, these are the pics:

Just rig the backpack with the spine bones.

What do u mean?

every model has got skin modifier where you assign each vertex to bone (or bones) and he said, you should assign backpack vertexes to one of spine bones (I think they are named spine1, spine2 or ValveBiped.Bip01_Spine1 etc. ) so you don’t have to make any extra bones