Bathroom odor only after motor home has been driven?

One other thing that caused my same problem.. there is a rubber seal under your toilet that can allow sewer gas to escape while driving.

If you have roof vents open it creates a vacuum in the rig. Many rigs are built with ' pop vents ' instead of plumbed waste tank vents. You would see that under the sinks, to the sides of the P traps. Popvents are supposed to work only when there is lower pressure in the tank than in the house, Maybe yours is acting both ways?

Pour some water down the shower drain and sink to fill up the p-traps which are used to prevent odors.

First thing to try - are you driving with any of the roof vents open? If yes, try it with them closed - I bet you'll have less odor.

I've had that before in my trailer. It only stunk after driving for a couple of hours. I took my paint roller extension pole and punched the stuff off the bottom of the vent vent pipe. It came out kinda gross but nothing a water hose couldn't fix.
Haven't smelled it since.

Sounds like you have a venting problem. I installed a device over the bathroom vent stack that cured this problem fro me. This is similar to what I installed. Clicky

Is the door from the sink? Is that trap empty.