Here is helpful information from Robert Bauder!
For removing the musty smell inside cases, you can
If the outside of the case is a durable plastic that is tough, it can be cleaned with the same solution.
One thing about cleaning the inside lining of the case would be to Now, "Why JOY?" Well, I'm glad you asked.
1) remove the clarinet (uhm, that kinda obvious) ,
2) use either some good upholstery cleaner or just mild Joy Dishwashing liquid mixed with water, not very much soap.
Joy is good for the soul and the Joy of the Lord is my strength. BUT Joy Dishwashing liquid doesn't have any additional additives that will tear up the lining or corrode any of metal .....believe me, I've done the Pepsi challenge with Joy and another brand and it's really really true.
- open the case and put it out in strong sunlight. Do this repeatedly or for a long time— as in, several days.
- put a dryer anti-static sheet into the case.