Trailers are not well supported online and I know of no sites for them!
But on this question, we never really knowwhere and how smellsget in but my thoughts were that once they got outside on the vents and being so far back from the cab,they were less likely to get back in whilemoving. They get left on the road behind?
So if they were not coming back in, the points that I looked at were where I thought they might come inside and into the cab area. I find little difference in black and grey smell, so looked for suspects in both.
AARG! I may have been doing too much guessing! I went with the early year and now looking at the later year, there is a totally rebuild/redesigned later model on the holding tanks!
If the 7th digit of the serial is 2,this is the correct layout for holding tanks and venting and it may be a totally different idea on the smell. The small basin in the stool area will also dump intot he black tank!!
That makes the trap at the basin a major suspect.
So some real close checking may be needed as we can mislead our self at times and jump the wrong way!
Question carefully if it is in fact only when the tank is not well rinsed or if it might be a timing thing that is really caused by the water in that small basin drying out so that there is no seal for odors?
This drawing instead of the first group!!!
If the trap is dry, there is direct access to the inside from the black tank. Rinsed or not may be more a level of smell, perhaps?