Sounds like your furnace is going into overheat. If making a large temp change in the RV, the furnace temp sensor will stop the flame if the furnace plenum temp gets too high, the fan will continue to run to cool the chamber and then the flame will then re-ignite. This is normal most times. If it always does that you may have an obstruction in the vents or too few vents.
U.S. Coast Guard retired- 1956-1985
2016 Siesta 24ST
1972 Moto Guzzi Eldorado