Scouring pads might work- frankly, if I was replacing fiberglass, I'd reach for 000 or 0000 steel wool.
Overall, it sounds like the quality of the kit leaves something to be desired. Do you think that's accurate, or is that just a skewed perception from us seeing what causes issues, but not along for the glorious rides?
Had it in the dirt yet?
Thanks for the after-build update! That's the crucial bit that is so often missing.