I'm a full-timer and haven't used any chemicals in the toilet in 8 years now. If your getting odor from the toilet it's a venting/seal problem as others have pointed out... simple as that. Correct the problem or continue using chemicals and then live with the chemical smell.
Ceiling vents, fans and A/C units can/will pull the smell from your black tank via the toilet if the seals are bad. Also make sure water stays in all your sink/shower traps, verify that all vacuum breakers are installed and operating properly to insure the smell isn't coming from your grey tank.
My MH came with a washing machine option and the drain pipe wasn't capped...
