Long running furnace & wheres the sensor

[2 DA WDS]

This weekend was our first campout with our current MS RE3 where the temperature got in the low 30s. I started out using the heat pump and discovered that apparently when it gets too cold it automatically switches over to the furnace. No big deal, kind of impressive. But, the furnace would run for quite a while then shut off for a minute or less then start up again and run for quite a while and then shut off for a minute and so forth. With all the insulation I am supposed to have I didnt think this was operating correctly but it did maintain a set temperature.
Is this the experience others have had in cold weather. When I had my Cardinal 5er the furnace didn't run nearly that often.
Also, I went looking for the temperature sensor in the lower level. I see the one in the bedroom under the cabinet above the window but for the life of me could not find one in the lower level. This is an 05 RE3 #1646. My other MS was an 05 RE3 #1850 and the sensor was under the cabinet to the left of the television. Can anyone tell me where the sensor is in this one?
Help me out here if you can.