I would assume that that they are made with the same mild
steel as the expanded diamond shape grates on most large smokers.
The biggest concern here that we've all seen and experienced is the sag factor of softer metals after they're heated. Think of the charcoal grate on a 22 1/2" kettle and anything else that has a long stretch between supports. Eventuallly the metal will sag in the middle from the heat, and gravity. If this drum has a center brace (left to right welded to the top and bottom of the drum), running under the cooking grate this sagging tendency would be lessened considerably over one that didn't have this feature. A piece of angle iron or channel iron should be used here.
Once the paint or protective coating is burned off and brushed very thoroughly, keep 'em greased and you should be fine. Unless you order stainless Lang's and others grates will rust if not kept lubed.
I'll agree with this. Don't clean the grate when you've finished your session. Leave it filthy. Just make sure you start your sessions with a blazing fire to assure you get the metal really hot to sterilize it and then brush as usual. You'll still have a rust problem (you're not gonna get away from this) but it will be much less than a grate that is cleaned after each use.
The same should be true of re-bar as long as it's not galvanized.
If it is galvanized this has to be removed 100% before use. Burning zinc is highly toxic to inhale, and this form of zinc is toxic to ingest. I wonder what it would cost to have these fired, and porcelain coated...My concern there would be that the porcelain on the ribs of the rebar would get worn quickly from turning utensils, and you'd have the rust anyway. Keep us posted, and let us know when the party is... We'll be there.