It is likely the furnace needs a complete cleaning. I refer you to the Atwood furnace service manual
, particulary page 21 of this 58 page pdf. for accurate information. My method is to first turn off the LP cylinder valves, then remove the furnace burner assembly so unobstructed access to the combustion chamber is possible. You already know about wasp nests, spiders are attracted to the odorant in LP gas and will build nests in the chamber, hide in the actual burner nozzle or block it with a nest.
While you are in the mode, consider also cleaning the water heater assembly too.
2000 Winnebago Ultimate Freedom USQ40JD
, ISC 8.3 Cummins 350, Spartan MM Chassis. USA 1SG, retired;PPA,Good Sam Life member."We the people are the rightful masters of both the Congress and the Courts - not to overthrow the Constitution but to overthrow men who pervert theConstitution. "Abraham Lincoln"