Well, we used the GEO Method and we are very pleased with the results. Before we left home for the weekend we added 2 packages of water softener, 1 cup of laundry soap and 2 cups of bleach to the black tank. We filled the tank about half full of water and drove to our campsite which was about 125 miles. When we got to the campsite we amptied the black tank before we setup camp. Once we were in the campsite we filled the back tank about one-third full and added the same ingredients in the same ratios. Already, at that point, we smelled no odors from the black tank. We were odor free all weekend.
Upon leaving the campsite we dumped the tanks and filled the black tank about half full and added the same ingredients one more time.
We probably didn't have to do that last one, but we just wanted to be sure. Anyway, we have no odor from the black tank.
Thank you all for your suggestions.