Well, theoretically, fiberglass is fiberglass, so an appropriately colored filler ought to do the job. It's not as if an electric guitar's body affects its acoustic properties....
The outside of the bass is presumably painted, and clear coated with paint very similar to automotive grade (enamel). I would bet that automotive polish would be just the ticket.
TEST IN AN INCONSPICUOUS AREA FIRST TO MAKE SURE IT WON'T SWIRL OR CLOUD THE TOPCOAT!!!
An electric guitar isn't fiberglass. If it's worth fixing take it to a good paint store that sells automotive paint and they will hook you up with the right compound and polishes. Don't go to a home improvement or auto parts store the stuff you want won't be there. Simonz is the the right idea just the wrong quality.
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No opinion about that particular product.
Ask a local music store what they recommend?
TEST IN AN INCONSPICUOUS AREA FIRST TO MAKE SURE IT WON'T SWIRL OR CLOUD THE TOPCOAT!!!
Cheers