You can set the tank on something else thin, it doesn't have to be the nubs. Think thin strips of wood, paint stirrers, etc. Just something to lift it up about a quarter inch.
Cover the top with foil to keep the heat and humidity in.
Any open-top enclosure will be a challenge to set up correctly if your room ambient temp is low, as you're fighting the laws of physics; warm air rises and takes the humidity with it, and glass is a poor insulator.