Well we located and solved the problem! (We hope...). Got up on the roof and located the sewer vent, removed a little sealant from the screw hole and took off the top. Found that the sewer pipe was about an inch above the rough cut out in the roof but well below the inside top of the vent assembly. It was also loose in the cut out with about 1/4 inch open and unsealed around the pipe... Well when I had the wife turn on the AC, air immediately blew out of the rough cut and around the pipe. I sealed the area around the rough cut and pipe with plumbers putty and backfilled the vent assembly around the pipe to secure it. I believe that sewer gas was sinking back down around into the roof/ceiling cavity and venting back through into the bunkhouse when we turned the bathroom fan on. Hope we're done with this issue... Thanks for the responses and hopefully this will help someone else. Happy camping!!