Cannot recall where this recommendation came from
When LAYLA came home from Philly in 2006 she had been laid up ashore for the two previous years and exhibited some funk as well. What was recommended to me for her next winter layup was Formaldehyde. The instructions were to place an open (disposable) container containing 8 oz or so in the cabin prior to closing her up. The next Spring a white powder residue was all that remained in the container and as I recall, there was little or no mold growth evident.
First thing I did though was to wash every exposed surface, the thought (after-the-fact) of having the residue of the formaldehyde was not desirable (or healthy)
Spring prep included oiling the interior surfaces and the following Winter I kept a bit of heat on to try and keep the humidity levels down, and still had some mold growth.
I'm inclined to agree that a varnish/ or urethane coating to seal surfaces is the long term answer where exposed surfaces are concerned. But what about the void spaces?
Just did some "googling" on related words and discovered some interesting data, including;
Bleach will not kill the mold but a good biocide, or anti-microbial will.
Bleach apparently does not kill the mold but rather cleans the surface of black or in our case the appearance of the green blush (fungi). When conditions are again optimal the mold spores remaining on or in the surface will regenerate and regrow.
Last couple of years I have done as David has, used Tilex to Spring Clean. Sprayed it on, let it sit, then re-applied and wiped down. The short term residual bleach smell at least makes you feel like you've actually affected something!
Before applying a permanent coating I have a problem in my interior, quite a dramatic difference in the colour of the wood veneers and new trim wood. Assume it's generally darkened from the years of oiling, except where there's been constant sun exposure. Our boat had the Plexi topped sliding hatch so there was constant source of uv all around the companionway, nav station, galley surfaces, etc. I've played a bit with water based stains prior to oiling for the season and they seem to just bleach out too readily. We now have a solid/ planked sliding hatch so that damage will be reduced.
Some advise in the past had been around wet sanding with oil to lighten the darkened surfaces, big job and obviously requires removal of a significant amout of surface to get down to the lighter grain. A continuing debate for another day!