Sounds like a problem I had a while back,,,, Make sure your regulator is working properly,,,If the pressure drops,, it will kick the furnace off,(excluding the motor).My regulator was approx a year old and it bit the dust,, it happens. ALSO,, check for Mud wasps nest and debri. I took my furnace completely out and cleaned it all out,, had a few hidden dauber nests inside the burner tube. You Tube has a few video's of what others have done and show what they have cleaned out of their furnaces.. And YES, Mud daubers can and will sneak through the screen and build a condo complex inside the furnace tube. Whats funny is,, during spring and summer,, they can build a nest in a matter of a few days,, And with furnaces, it dont take much to throw them outta wack. Good luck,, keep us posted what you find.
Thermocouple is my guess if you have enough LP gas pressure to the line. A lot of those are the 12v furnaces by Suburban that need about 11 lbs of pressure to operate. The termocouple going bad would cause the pilot to go out and stop the heater portion.
Found this to be one of the better suppliers with diagrams and such. I have a Suburban NT24M I'm working on now.
Just FYI and something to look for on this subject, David Craft hit on a good point to look for.
While I was doing the tear out of all the bad stuff in a water damaged unit, I happened to look under the couch/pull out bed. The heater duct from the furnace to the register vent had been almost completely crushed closed.by the couch frame that was sitting on it. It was probably only allowing 20% airflow through it. Also the register vent, located at the front and under the couch was partially blocked by some eons old shag carpeting.
It's hard to believe any heat got through this RV at all. LOL