The key is taking care of the holding tanks and not allowing them to get too full or not putting enough water in them. We use Thetford Campa Chem chemicals in our toilet and it never stinks. We put 2 small bottles in with a gallon of water after we dump the tanks. We use 2x the min amount because we are usually in hot climates. In cooler weather you could get by with one small bottle. It also depends on the size of your black holding tank. We've been full timing for 6 years.  Also the grey tank needs attention to prevent odors. Many times the grey tank can smell worse than the black tank!!  We use 1 cup of Dawn Platinum detergent and one cup of Borax powder mixed in 2 cups of hot water. We treat the grey tank each time we dump it. We also do not put food or grease down the kitchen drain. We are very careful to wipe out the dishes and pots-pans before we wash them.  I agree with you. The bathroom is one of the reasons we have an RV!! "Go" for it! LOL