The two best things I've found to use on a fiberglass stall is either baking soda or Bon Ami, on a dampened cloth, powered by a lot of elbow grease and lots of rinse water. It's a pain in the patootie, but it works and makes the fiberglass shine like new if it isn't all scratched up. I'm not sure it'll work on the copper stains, I've never had that problem.
By the way, the rough finish on the bottom of the shower can be cleaned much easier by putting quite a bit of baking soda or Bon Ami on it, mix it with a little water and, with a brush, scrub, scrub, scrub… rinse, scrub again and repeat until the nasties are gone.
Best of luck on this one. It's going to be, at the least, a mild pain.
Donald replied
269 weeks ago