Had a somewhat similar problem with my 97 Land Yacht WB diesel. Furnace blower would cycle on as usual then you could hear the burner trying to light. After 5 automatic tries it stop till the main switch was reset off/on. The furnace would never stay fired up longer than 7-8 seconds.
RV mobile tech found the computer board, located outside, was defective. $125 later it was like new. In fact, tech said the furnace itself appeared to have never been in use. Considering the rig spent it's whole life in NC and FL, I suspect first owner only used the roof electric heat when necessary. That just was not enough heat for me in Montana