If you are really doing the things you SHOULD do to control mold
on a boat, mostly VENTELATE, running a filter is going to have a placebo effect at best. You should be moving so much fresh air into the boat that the filter is basically cleaning
the whole outdoors. The sound of the running fan might make you feel better, but that is all it is doing. There is no way you can expect hepa filtration to reduce the number of mold
colonies. I'm not saying you're mistaken about WHAT happened, just the WHY part.
Another point to understand is that a high level of ventalation not only helps eliminate the conditions that cause mold to grow, it also dilutes dramatically the concentration of airborn mold spores in the boat's living quarters. Mold spores can be a health
hazard in an enclosed space, a properly ventelated boat is by no means an enclosed space!!!!