Getting back to the 1070, I just spoke to RT tech and asked some general questions. The 1070 body is 430 SS, The fire pot, drip tray, and grates are all 304 SS. The main difference between the 590 and 1070 structurally, is that the auger tube and fire pot are below the barrel in the 1070, whereas they are in the barrel on the 590. Which allowed them to make the narrower hopper deep enough to hold 30 lbs of pellets. Good idea anyhow, as top of the fire pot is flush? (not sure about that) with the floor of the barrel. He said that there was really not heat loss from this position. (I guess because the fan blows the heat upward). The 700 has the tube and fire pot above the barrel floor.
Also, the 1070 body SS is 16 gauge. While the Memphis BS body is only 18 gauge! (Memphis is mostly double walled however).
Just FYI.