If you don't look forward to tiny fiberglass needles in your skin and breathing toxic vapors, consider Nudo Polymetal or Grimco Max-Metal as a material.
These samples were sheared, rolled and braked with a hand operated tool with an 18" lever arm. Braking the short edge ruptured the metal skin on the outside. Scoring the inside first might alleviate that.
The result is pre-finished, no filling and sanding needed.