We have Dirt Daubers that will get into any opening and built mud nests. The nests can weigh several ounces and the daubers seem to love fan blades. I had one build a nest in the AC of a cabover truck camper several years ago. When I turned it on it shook the whole camper. If you haven't allready done so cover all openings furnace, water heater, frig, etc with screen.
2010 Rockwood 2604SS
2008 Silverado 1500 LTZ 4X4
Great Wife and Idiot Yorkie
True Friends are like diamonds, precious and rare.
False ones like autumn leaves found everywhere