rodebiker,
The thermister i what you control the temperature with. It should be mounted on the fin all the way, you move it up for colder temperature, and down for warmer temperatures. For the most part, once you find the sweet spot you can leave it in one position. Like Dan said, with an RV fridge you've got to allow air to move around in there. Some people get the little battery operated fan to circulate the air. If I remember right, it should go in the bottom of the fridge, as the air is colder there. Also, again if I remember correctly, for every minute the door is open, according to a seminar I went to, it'll take 1 hour for the fridge to get back to the temperature it was at before the door was opened.