you stove first to make sure that the lines have gas not air.
2 try firing up the furnace, if it doesn't light
after a few tries, then I would pull the unit and check the sail switch as the gas will not turn on if the sail switch for the fan does not activate properly.
3 If that doesn't work you may have a plugged jet.
4 pull the unit and check for dirt and bugs
They are a pretty easy unit to take apart but if you are concerned about servicing it then yes have a tech check it out.
I did make up a doc showing how to change out to newer style fans on the Casita
forum and have included it. It shows what screws you take out to remove the unit. BTW the newer fans are much quieter that the metal ones.
Sorry the pdf is too big to post, PM me if you want a copy