You might also try venting the whole structure as you build your next plane. I believe mildew starts from trapped moisture which can't evaporate thus creating an ideal environment for the mildew fungus to start growing. I also agree with tpstory that spraying the entire structure with polyurethane will help seal up the wood and help preserve the structure.
I always disassemble my planes so they can breath when I'm not using them. I'm sure boat builders, especially those in coastal areas have a few tricks to prevent this problem.
My current project is a twin engine, scaled-up Aqua-Star for two 25's. I hope to keep this plane for many years so preservation is a priority topic.
Lets keep this thread alive because I for one would also like to have a few tips on this matter.
Peter