I have a feeling that your waste pipe from the toilet may be too long and the only thing that should do is reduce your time between dumps. You may have to measure your black tank height and the compare that figure with the distance from the bottom of the waste to the bottom of the tank.
I had a similar problem with my newly purchased Winnie and I did a really great flush, cleaned and lubed the flappers in the AAVs, replaced the seal in the toilet(the bowl wouldn't hold water)and no more odor. I have a Tornado flush system. I also have a hose flush fitting on the elbow from the knife valve.
No odor.
Good luck.