Well, I quickly located the sewer vent pipe using the smell test
It was the one directly over the tank as expected. Still not sure what the vent at the very front of the camper is for. Anyway, I installed the Cyclone vent but unfortunately there was no noticeable change in the odor issue. The sewer vent is very close to the bathroom roof vent so the odors may be coming in the opposite direction from what I'd imagined. Oh, and if anyone decides to install one of these, do not pull up on the top of the Cyclone vent to remove it from the pipe! Mine separated and was very difficult to put back together again.