First full season with our Big Country 3450 and loving it! We have owned several travel trailers and they all had an air intake for the furnace inside the coach with some kind of filter. Most had a washable one like the AC uses. We seem to be having alot of dust in our coach after the furnace shuts down. I went looking for the air intake in the coach and for the life of me I can't find it??? Is there a filter somewhere? Is it possible to add one?