We have owned a 27' bumper pull, a 27' fifth wheel with one slide, and a 37' fifth wheel with 3 slides. Every one of them had 4 heating registers. My point is that the 37' fifth wheel needs more but the industry is too cheap to put them in. The 37' was the only one to cycle like the OP. I absolutely believe that it is an issue of inadequate air flow through the furnace. It has not been an issue when the furnace is cycling to maintain a temperature. It only does it when the furnace runs for long periods such as raising the temperature in the trailer. I haven't decided if I'm going to try to improve the airflow. If it quits cycling the flame on a long run I will be concerned that the temperature switch is not protecting from an over heat situation.
