While we generally use racks now and humidity is not an issue we do have one display type rack that I home built. To keep the humidity up we just keep the humidity up in the room with a humidifier. Granted where we live compared to you it is a lot easier. One thing we do when ours our in shed to bring humidity up is move the water dish as close to the heating element as possible. Also we will add additional water dishes if we have issues, but only had to do that one time during the winter.

As for the hides for our larger ball pythons we use large - jumbo plastic mixing bowls and they seem to really like them.