It's a question that must be asked: Is it better to clean? Or is it better to paint? Or both?
When the subject is a compartment that has mildew deeply embedded in a rough fiberglass surface, the answer is clear, and empirically proven: Paint.
The compartment above is against the hull. That is, the back wall in there is actually the hull itself. In the winter, that hull surface is nearly the outside air temperature - because the compartment is full of Jane's clothes (in Tupperware boxes and plastic bags), so there is little air circulation. But the moisture finds its way to the hull and condenses there. Consequence: mildew.
For you purists out there, I first tried cleaning the surfaces with bleach and water. It worked, sort of, but was slow and messy. And it was clear that when I was done, another coat of paint was still going to be needed anyway.
So I just got out the Brightsides - I love this stuff! A single coat completely covered the mildew. And surely killed it. I wore an organic vapor respirator while I applied it, by necessity - I won't be sleeping in the aft cabin tonite! The paint fills in the surface roughness that the mildew loves to hide in, leaving a beautiful, smooth, shiny surface.
And since the aft cabin is off limits for a while, I'm going to also sand and re-varnish the sole in both the aft cabin and the aft head after lunch. But that's another story.