Seems like every time I have to repair a seaplane, when I peek under the covering there's an infestation of mildew. Today, I opened up a previously undamaged wing that's only been on a seaplane for 2-3 weeks, and it's got a load of mildew in it.

What can I treat the balsa with before construction to prevent mildew? (It must not prevent the covering/glue from bonding to the balsa)