Re: Musty boat smell under floor
"or using spa chlorine tablets in the bilge..."
Minne, I've had the same temptations to pull a blanket over the keel and chuck the tablets in to kill critters. But also the same reservation, chlorine tends to make things come apart. Stainless keel bolts should prove that very quickly.
A musty smell is likely to be mildew. Plenty of threads about how to get rid of that. Clean it, dry it, keep it ventilated, no magic there. No shortcuts, either.