removing laquer from fiberglass

I find that the ethanol in fuel,( petrol) damages old bike tank lacquer.pre 2 pack ,worth a try

Removes the fibre glass as well!

Cellulose thinners is just about the strongest solvent available - it melts many plastics and strips paint, but with careful use you could strip the top coat.  What you need is a rag you can use with thinners on and another rag with some white spirit on (or your favourite drinking Meths!).  You apply the thinners and quickly wipe it off!  I have used it successfully on uPVC, but as  they always say, test it on a piece that won't show first!

Experiment carefully - in a well-ventilated area!

Don't use solvents. Sand away carefully with a fine wet paper. If you can't get it smooth without rubbing thru the gelcoat, stop and add more paint with a high-build etch primer. Or, if it's really bad, body filler. If the gelcoat itself is bubbling up, then knock off the loose stuff and fill.