Bottom: 40mm high-density mineral wool, jute, or fiberglass 50 kg/cu.M or isocyranurate foam. Insulation supports weight of food. Rug or carpet second choice. Scrap textiles, raw wool, or cotton need spacers between interior wall and case.
Sides: 40mm low-density fiberglass, mineral wool, jute blanket 12 kg/cu.M will conform to the irregular shape of the sides. Textile cuttings, blanket, rug, or carpet will remain vertical on sides.