Our sturdy parrilla barbeques are made of mild steel. Yes they can rust but we recommend leaving the grease on them from the cooking process as this protects them and the fire sterilises them prior to the next cook.
Stainless steel is not suitable as it does not conduct heat as well as mild steel. The main difference being a typical barbeque and a parrilla is the grilling surface. Barbeques tend to use a wire mesh, often in stainless steel. The drawbacks are the fat tends to drip on to your coals which can cause excess flame or even extinguish your charcoal. It also creates a lot of mess.
An Argentine parrilla uses a V- shaped angled steel which collects and holds the grease and fat so the flavour is not lost and the meat does not dry out during the slow and low cooking method.