I'm sure others will chime in, but right off hand two things seem odd to me. The uth wrapped in aluminum foil, and the thick layer of aspen. Many people just use a thin layer or even a just a few sheets of newspaper. It seems like you are insulating your tub FROM the heat source rather than insulating the tub from the outside air. Humidity can be raised by increasing the size of the water bowl and/or moving it closer to the heat source.