Mold propagates from spores ... found commonly in the atmosphere.
To control mold you must
1. remove the mold from ALL places from where its propagating ... including all the hidden spaces, all the space UNDER and behind whats 'visible'. You have to clean/kill/remove the 'fruiting bodies' that produces the 'spores', its the spores that cause to 'spread'.
1a. Mold has to be REMOVED not just 'killed' as successive invasive species (other species of mold, mildew, bacteria, etc.) will use the 'dead' cells as their nutrient source . Mold is 'best removed' by dissolving it
using caustic products to break-up and liquify the cells. My favorite 'boat caustic' is Tuff'eNuff a sodium silicate based detergent - common in boat chandleries on the East Coast but can be special ordered from WM, etc. - EXPENSIVE!.
Mold shouldnt ever be 'disturbed' when dry ... as that will only 'broadcast' spread the spores. You MUST wet-out the mold (spritzing, etc.) before 'disturbing'. Some mold species and spores are VERY dangerous/toxic when in contact with your respiratory tract - you MUST use a mask or respirator, and mold or mildew that is 'black' should be under extreme suspicion of being VERY DANGEROUS.
Cleaning includes the VENT of your water tank - a most ideal container for the growth of mold and its spores.
2. Prevention .... mold spores will NOT propagate on 'caustic' or alkaline surfaces. Our ancestors covered 'everything' possible in white-wash and hardly ever had a mold/mildew problem. A modern form of whitewashing is to 'spritz'/spray highly-caustic detergents on those chemically compatible (non painted / non-bare wood / non-varnished) surfaces and simply let dry.
2a. Avoid oil based wood finishes and 'soaps', etc. ... simply FOOD for mold.
3. When closing up the boat for long term storage, consider to use ParaFormaldehyde Crystals --- sprinkled into a heap on a glass plate. The crystals will develop into a
gas that will prevent spores from 'activating'. ParaF gas is also VERY toxic to human lungs ... so you need to hold your breath and thoroughly air-out the boat before removing the crystals. ParaF will certainly not be available in areas where the 'environmental' activity is high.
You can temporarily keep mold under control by wiping painted/varnished/bare wood, etc. surfaces with vinegar, clorox .... but must be repeated 'often' to keep the surface 'acid level' higher than what will produce mold/mildew growth - although molds/mildews prefer slightly acidic surfaces, etc. for accelerated growth. A good 'killer' is Tile-X but may 'bleach' some surfaces or 'raise' some paints
, etc. if left in long contact.
If you want to control and prevent mold, you must return the entire boat including all the hidden and inaccessible spaces to a sanitary and 'hygienic' state (good luck with that if your boat is 'pan' or 'molded liner' construction).
Someone mentioned oxyclean + peroxide is OK; but, there are stronger and more effective 'killers' ... but you really need chemical and chemical safety expertise to use them (mixtures of peracteic acid + peroxide, quaternary ammonium compounds, etc.) You must either know or have to remember that fungals have a quite similar cell structure to humans/animals so what kills/dissolves mold/mildew can also do the same thing to human tissue/cells, etc.
Complete 'Hygiene' is the solution - you eventually and periodically have to clean/scrub every damn inch inside the boat. Mold thrives on exfoliated human skin cells and each human body sheds 'zillions' per day.
Wear your 'mask' or respirator.
hope this helps.