I'm not that experienced in PSA but I'm pretty sure that if you want a hitbox to follow a bone, it will be attached to wherever that bone is as long as you put a hit box on a bone and for however many frames you set it to before you terminate collision.
First pic is ZSamus' leg bone with ID in BrawlBox BoneID is 62
Second is converting ID into hex using windows Calculator
Last is how the hitbox follows the bone for her Dash Attack
Bone 3E, 3F and 40 are her leg, knee and foot. The hitbox stays on the bone until you terminate collision. I hope this helps and makes sense. If I said anything wrong feel free to correct me.