I used my steam vapor cleaner to clean 20+ years of diesel, mildew, grime, slime, and generalized yucccchhhhhhh off the fiberglass under my cabin sole when I pulled the sole to refinish it. I didn't want to use any chemicals as it was a large area, and I would have asphyxiated myself if I used anything. It worked like a charm.
Clean, no smell, no toxins.
This spring, I used it again to clean my deck with similar results.
If you get one, get a good one (not 'as seen on TV), mine is a 'vapor clean tr5.' They are pricey, but you can frequently pick one up used.