Every time we tow our hybrid when we get to the site or get home we had a bad sewer odor in the camper. Just open windows and turn on the fan and its gone in a few minutes. I've tried towing with the ...
If you dump before you roll down the road... make sure you put water back down the bathroom and kitchen and shower drains. Sometimes the traps get sucked empty when you dump the tanks.
Close the vents in the rig before you dump. If you have the ceiling vents open (and the fans going makes it even worse) you can suck smells up into the rig when you dump.
and close your ceiling vents when you roll down the road... see if that keeps the odors "down below".