From my dim memory of boats (low cost plastic ditch crawlers as GRP was known). The gel coat needs etching and the paint might be cyano-acrylate. A phone call to Tankards at Weir quay if they're still going should get you an answer.
Ian I've found a really good painter & motorcycle guy up near me, Terry. He has a couple of rather lovely Norton cafe racers, he's just restored a WD 16H which is immaculate, he does something once and does it properly every time, a perfectionist. He's just done some painting for me, which included a fiber glass seat unit for my cafe and he's done an awesome job, he actually re-did somthing another painter I used did and ballsed up. He's resprayed a Honda BlackBird recently that was also his and that was stunning too, he's the kind of guy you could ask 07900 934634. I won't be using anyone else for my painting, he is very helpful and no-doubt will tell you.
Hi Kit...Thanks for the tip but I generally do all my own spraying...I just need any relevant tips on the preparation and primers needed for fibreglass which I haven't sprayed before...Ian
I spent many years working on caravans, and when getting them ready for paint I usually sanded the gel coat down with something fairly course, approx 400 grit, then gave a light coat of etch primer, then usally a high build 2 pack primer as the fibreglass was never the smoothest of surfaces. I usually rubbed this down with some 1200 grit wet and dry before the top coat (using panel wipe before application of top coat).
I never had any complaints and never had any problems with the paint not adhering to the surface. Other people might have different opinions but this always worked for me.