Yes finding the source is also the key, but good ventilation will help to prevent mold growth.

When I first got our boat, there was always standing water in the bilge and the boat had the typical "boat smell."

Since then I have replaced various seals, I don't allow the ice box or shower to drain into the bilge; the bilge is bone dry, and I have cleaned the solar vent... About the only smell I get these days is diesel... while lingers from running the engine. I also prop up covers and cushions when I leave the boat, and we only flush with fresh water.

I also plan on replacing the solar vent for one of the newer 24 hour ones.

Now I have a small boat, so one vent seems to work fine. But for that 38 footer, I'd bet two or more vents should be used.