Insect screen over furnace exterior vent can save big money

I've held off putting screens in or on because of cautions from mfg.
However one of the furnaces, fan was making a racket. It had a mud dauber nest on it.
Wouldn't hurt to have them on the furnaces, in summer. Pull them off when cold so no ice forms on them.
Maybe some kind ,of stick on base, for when you are parked and not using the RV.