Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4806355.

spaces between inner and outer wall fill with sand , plaster or epoxy

https://youtu.be/eOXZrhc-rW8

(Donations appreciated, but not necessary. My things are free and will always be). <a rel="nofollow" href="http://paypal.com/paypalme/syzguru"><img src="https://cdn.thingiverse.com/assets/7d/eb/01/09/f6/large_display_buy-me-a-coffee-with-paypal.png" alt="Foo"></a>