2012 Rockwood 5th Wheel Suburban Propane Furnace Question

I repaired my father in laws above mentioned rv today. The propane furnace was not heating. I found the over temp limit switch had opened up and was not allowing the burner to light. Replaced the limit switch and all seems ok. But I noticed while buttoning up the covers around the furnace which is mounted in the belly compartment the outside metal cover where the flexible ductwork is connected seems very hot to the touch. I assume its normal but thought I would ask as I have never monitored how hot the furnace shell gets while the furnace is operating. The blower wheel appears to be spinning and pushing air through the furnace normally.