The measures described are good.
Since you are allowing for make-up air, look into a central exhaust vent set up an a de-humidistat. You can probably get what you need for under $500.00.
One company you can check with is:
DEC International, Therma-Stor ProductsP.O. Box 8050Madison, WI 53708800-533-7533
I've used their Quietvent on a number of projects for similar problems as you are having.
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