Any of the products mentioned will work in getting the exhaust residue off of the fiberglass. I have always found it a challenge in getting it off of my stainless exhaust. Best solution so far is soft scrub without bleach. It comes off pretty easy. I then follow-up with a good stainless steel polish. Soft scrub is mildly abrasive and it does not scratch.

I'm using a boat soap from west marine that has orange in it. I think its called west marine boat soap Seems to be doing fine on both the gel coat and the vinyl graphics. Removes spider sh!t instantly too.

Spray nine has always worked for me...

Use Fantastic with orange,it's a kitchen product,ask your wife or girlfriend,she knows what it is .It works.If you got a scum line after you pull your boat just walk around and spray on and wipe scum line off. Also if you have spotted stainless tailpipes or yellowed stainless exhaust headers,use Blue Job.You can get it at your local motorcycle shop,or order it direct over the internet.Use a dab of water with it,your pipes will look like new.

Thanks for all the help guys. Gotta keep her clean back there.