Since a SS works by trapping infrared heat I wouldn't expect that a flame-less BBQ is going to work very well. Most of the IR heat will be radiated straight up. Conversely, an open fire with lots of flames will radiate a lot of IR sideways. If you only have one SS, then putting some type of reflector on the other side should help quite a bit.

Also, facing the shelter toward the sun (if available) should also provide a lot of IR heat, even without a fire.