I havent read every response and I dont know what kind of tent you have or how much space is in there but what about a low tech approach? Might be difficult and darn sure time consuming but what about heated stones? (The type that dont explode when heated. Like sauna stones.) Maybe warm some in a fire nearby and put them on a platform in the tent. Then either leave them inside to radiate the heat or allow the water to drizzle onto them and make steam just like they do in a sauna. Just an idea.