As others mention, make sure there is water in the toilet bowl.
ALSO - run water in all sinks, showers and drains for about 10 seconds to make sure there is water in the p-traps. All the bouncing around while on the road can slosh the water out of the p-traps.
Verify the roof vents are clear and not plugged, You may need to remove the vent covers and use a long snake to make sure the vents are clear.
If the odor continues, look for broken pipe connections, on the tanks.
If worst come to worst, replace the roof vent with a sewer Cyclone
WINTERIZING / DEWINTERIZING | 2001 Coachmen Mirada 300QB