Did you find and correct the smell? Has anyone installed a Fantastic Fan? Using it like an attic fan for complete air exchange.
2 things I've done for freshness.
1. Just before travel... Add a cup of cheap dishwasher liquid and a gallon of water to the black water tank. The swishing action cleans the tank nicely. And dump it before setting up camp.
2. I took down all of the airstream drapes. I think they are wonderful, but they were old, faded and mildewed. So...I got a 5 gallon bucket and filled it about half way with undiluted Clorox bleach and put the drapes in it overnight. Like my husband said, they were already ruined, so the worst that could happen would be trashing them... Well, the next morning, they looked brand new. I machine washed them and hung out to dry. They are fresh, clean, and the "downy" softener I used in the machine, leaves a wonderful smell that has lasted.
So... hope you were able to solve your smell problem.