Sewer smell when using exhaust fans

Check vacuum valve under sink and close gray valve you are sucking sewer gas in from sewer system.

It serves no purpose to use a deodorizer for grey water - if the valve is open ,there is no water in the tank to deodorize.
The smell is coming from the sewer up the hose into the camper.
It can only get into the camper if the P trap under the kitchen sink/bathroom sink/bathtub/shower has no water to block the vapors or if the vacuum valve under the sink is not sealing.
The valve is cheap and screws into a fitting and is the likely culprit.
It will be free to replace if you use the money for deodorant on it :)

Try closing the gray line.

Here is Yuma our sewer line has significant positive pressure. You may have enough that the gas is able to get through the traps.

I always left both closed then I had some gray water to flush the lines after dumping the black tank.

Did you check to see if you have an Air Admittance Valve under the sink?
Maybe it's bad.

If you have a traditional trap under the sink and there is water in it then that should stop the odors but if you do no and the gray tank is open there is nothing between you and the entire system. Either close your tank or put a dip in your sewer hose to create a trap to see if this helps. Another idea is to put deodorizer in the gray tank.