Both the above posts are steps to follow as your coach may have a p-trap or a HEPVO valve. Either one can be found in a shower drain. Someone with the same coach may be able to tell us.
Point is, there should be no odor from the drain unless either one of those devices is dirty or faulty.
Larry, Eileen, and Finley
2004 Alpine 36FDDS
Third motor home, first Alpine, no need for another.