1. Mount it on the bottom. The snake will make more use of the uth that way.

2. Tape it to the outside of the uth. You don't have to sandwich it between the uth and the glass. I never do. Just make sure its secure and won't fall off.

3. The rubber feet that come with the uth will raise it enough to promote airflow. It will never come in contact with the dresser. Since you will be controlling it with a thermostat. The risk of fire is extremely extremely low. The lamps are more likely to catch fire at that point lol. As for scorching or discoloring the dresser? Its only going to be 90 degrees at the hottest... That's not nearly enough heat to do anything to the dresser. I don't think you need an extra piece of wood.

Think about it this way...if the uth was hot enough to damage the dresser...the snake would be cooked.