I used the Geo method with good results ... until the season lease. The problem was the accumulation of toilet paper in the tank. Now I use Calgon powder to soften the water and help it flow better but also use digester for the paper. Since the trailer never moves I can't count on the trip to mix things up and get it moving. Never had an odor problem no matter the trailer nor the method.
I'm no expert but suspect that those that don't fill the tank until full are going to have a problem removing the toilet paper. It takes alot of water velocity to move it since it mounds right under the seat.
Using the black water flush it usually takes one or two times to get rid of the brown color but several more attempts to get all the paper out.
Gosh, what a pleasant topic
BTW, I'm beginning to have an issue with the valve not sealing after flushing. I can't see any paper attached to the valve or the sides of the toilet. Any suggestions appreciated.