I've posted on this product before, but thought I might again to let some of the members know there are other things to try.
I installed the Blue Streak Chem system in both the motorhome at work and my Mountaineer. It is an auto chemical dispenser which adds chemical as you flush. You use their chemical which is about $8 per quart. I'm still on my first quart after a full week out and a couple of weekend jaunts.
It works great for both applications. We spent a week in Kentucky in June and had the unpleasant task of having to pull the stool twice to replace the seal and the flush blade as it wouldn't hold water in the bowl. I didn't dump the tank prior to doing it so the top of the tank was open. Temps over the week had been in the upper 80's to around 90 with humidty. Toilet is used by 2 of the 3 kids and my wife and I. Even with the stool off, there was very little odor from the tank.
Nope, no financial interest in the company, just real happy to recommend a quality product.
http://www.bluestreakchem.com
Aaron