My furnace takes a bit of time to light if the gas has been off for a while. My gas tanks are on the left rear and the line goes all the way forward then crosses to the right side and back to the rear of the camper. Progression from the tanks is stove, water heater, frig, furnace, and then generator. I usually lite the stove just to verify I have gas and then the furnace or generator will pull gas to the right side. It has taken 4 to 6 tries to light the furnace.
Also, you may already be aware, if the furnace tries to ignite and doesn't get gas it will time out after some period of time and shut down. You then need to push the thermostat all the way back to the off position to reset it. There's a small switch on the thermostat that disconnects in the off position resetting the control board. You may have to give it 15-20 second. Turn the thermostat back on and the furnace fan should come back on. After a period of time you should here the igniter clicking. (can here it better from out side. It only does it a given number of times and then stops)
If it doesn't lite, turn it off for a bit then back on. Each time the blower should come on. Repeat until the gas gets to the burner.
If you have a generator at the end of the gas circuit try it a few times to pull the gas through the line.
Good luck.
