First, Not all molds and funguses 'stink' during various stages of their life cycle; would you eat a mushroom than 'stunk'?
Second, the mycelium are filamentous and are the vegatative portion of the fungus, meaning they produce small microscopic 'strands' that penetrate deeply into their nutrient source and usually only become apparently visible when they enter the 'reproductive' or spore forming phase; you generally dont see mold or fungus on food, etc. during most of its life cycle ... only until it is producing spore producing 'fruiting bodies' which happens primarily during reproduction cycles. When you see mold or fungus on a surface it usually means that its fully 'fed' and is now reproducing and generating spores.
Third, fiberglass is not a total complete barrier to water vapor, air and other fluids, it is somewhat (to a lesser degree) permeable to most small molecular sized fluids. A simple crack or other pathway into a void filled with wood, etc. would present a large potential of the mass transfer of air, water (vapor), etc.
Lastly, your blob 'looks like' an Aspergillus or very similar species .... and I have about 30 years of actual experience within the bio-tech / pharmaceutical industries in the growth of such in huge volumes of 'cell culture', one of my functions was to separate/extract them from their nutrients, etc. and contain them within their growth vessels.
So, to me this looks like an Aspergillus or similar species that is now approaching its reproduction phase.
Most aspergillus, penicillium, etc. species are usually only 'mildly' toxic, especially when they are producing spores, .... but some are quite highly pathogenic. There are literally thousands of such species. As posted previously many aspergillus species thrive in cold/cool conditions.
