The problem you have is that the foam has absorbed the chemicals. Since you cannot wash the foam effectively, as you did with the coverings, time is the best way to remove the smell. The chemical compounds that have been absorbed by the foam will dissipate into the air over time and the smell will diminish. If you add other chemicals to mask the smell, you will still have the problem, only masked by more chemicals. Other than that, you can take it to an upholstery shop and have the foam replaced. Not what you want to hear but mothball smell is hard to get rid of. Just ask my grandmother....
Take care.