Physic Asset for Human Characters (Low Poly)

I have multiple skeletal character meshes. It’s a very simple skeleton. No fingers. What’s a good starting point for creating a default rag dog asset for all my characters? They are all weird by default if I try the default create the physic asset from the importer. There are weird problems like the head falling off and rolling away. I don’t know any good tutorial for creating a physic asset for humans.