As suggested.......may have to attempt lighting it off a few times if propane has not been used----furnace not run---in order to establish flow to furnace.
Can you hear spark electrode clicking?
Does circuit board have an LED...it is ON or blinking?
Spark from electrode needs to be strong and be right over burner slots.
Check combustion intake & exhaust vents.....any obstruction then main flame can't light off (air/fuel ratio not met)
Here is a generic Furnace Troubleshooting Guide......rv furnaces all work same
LINK