Looking for ideas on the best material to fill a prop with to give it added weight? I'm used to dealing with solid resin or 3D printed props but I have come across one that is hollow and would like to fill it. It's a fairly narrow space. I need something that can fill it in and won't rattle around after I seal it. I thought about using some Great Stuff and filling in with some bolts but I'm looking for a better alternative. Any ideas are welcome!