Solar powered fans might do the trick. If you can keep air moving through the
boat, you will reduce the tendency for little green and black critters to grow.
There are formulas that identify exactly how many complete changes of cabin air
should be accomplished every day.

Now that the mildew has a head start, you will be faced with the problem of
arresting its progress and killing off the present growth, in addition to
bringing enough air aboard to reduce humidity.

You might wind up stripping the carpet or fabric lining from the inside of the
hull. If you have to do that, consider fairing and painting the hull instead of
covering it back up again- or if you must recover look for a meshy fabric- like
maybe a dressy burlap.
Critters will thrive on moisture trapped between a hull and a lining.