The one we use is not lined with any metal at all………its all wood. (like the assembley inst. for the commercial unit) The only Metal in ours, is the 3/8 steel lid, and the double steel rack that we sandwich the pig into. DOES NOT HAVE TO BE ALUMINUM! In fact I feel like ours was some type of re-bar. The rods are appx. 1/4 inch. If you can keep it from rusting and get a couple of roasts behind you, the piggy juices will protect your rack (season it).