The warm place has had about three days to come to an equilibrium. The outside temps are about 50 F. Inside temp stabilized at about 68 F. Warmer, but not warm enough. My target temperature is 80 degrees F. The water in the tub is clearly +80 degrees. On the plus side, the humidity is positively tropical.
I cannibalized a fan out of a broken microwave. Wired it up to the cord that supplied the microwave. It is now in the re-purposed refrigerator.
The only unfortunate thing is that the air blast is not pointed down toward the surface of the water. I tried flipping the fan over the but shroud was too short to protect the blades from the metal grating that forms the shelf.
My thinking is that more air blowing by the tub will improve the transfer of heat to the air.
I will see what the temperature is tomorrow. I also need to start thinking about how to handle the condensate. Humidity is good. Liquid water dripping on potatoes is not.