I use these, not exactly fire proof but they work nicely and are double walled. Just don’t stack to the top or the boxes/packs on top can get crushed.
BOX USA 15 Pack of Heavy-Duty Double Wall Corrugated Cardboard Boxes, 20" L x 14" W x 12" H, Kraft, Shipping, Packing and Moving
https://www.amazon.com/dp/B01BGFWY8S...ing=UTF8&psc=1