A common source of bad odor (especially the dreaded "rotten egg" smell) can come from the water heater.
If you ever store the camper for more than a week or two, be sure to drain the water heater to avoid that smell.
To deodorize the holding tanks, we really like "Simple Green" because it's pretty cheap and we like the powerful pine smell. (Anything with the name "RV" next to it seems to cost 5-10 times more than regular stuff, it seems!!)
Rick & Karen
(Retired USAF, MSgt)
5-year Travel Trailer RVers
2013 Forest River Rockwood Ultra-Lite 2904SS
2014 Toyota Tundra Maxcrew SR-5 TRD 4x4