I’ve been around some fiberglass
boats that had fuel, oil
, sewage, and whatever else imaginable swirling around in the bilge
for many years, with no ill effects.
FRP is a plastic, and there’s a reason that so many nasty products come in plastic containers!
Not to say that it’s ok to have a dirty bilge.
My boats bilge takes on a bit of water
from rain and spray, and always has some water
sloshing about, so I regularly throw in a bit of dishwashing soap, and it’s always pleasantly clean and odor
free when I have work
to do down there.