You may be drawing your odor from the roof vent pipe. Probably your grey tank which can smell as bad as the black. Sometimes worse because it get flushed seldom. When you turn on the vent fan it changes the pressure inside to draw low lying air from your roof inside from any other open vent. You can get caps that eliminate this; I bought some at a trade show they look like a white Darth Vader hat, they revolve in the breeze and carry odors away form our roof top.
Camping World has some and if you Google it you can find what you need.
I do all my own stunts
03 Dolphin LX 6355, Workhorse W22, 8.1 vortec, 04 CR-V, Blue Ox, Brake Pro----Norm, Barb and
Doc(He's a PhD)